diff --git a/apps/theming/composer/composer/autoload_classmap.php b/apps/theming/composer/composer/autoload_classmap.php
index a68410ce3ce28..9b53c0f9fea27 100644
--- a/apps/theming/composer/composer/autoload_classmap.php
+++ b/apps/theming/composer/composer/autoload_classmap.php
@@ -17,9 +17,11 @@
     'OCA\\Theming\\IconBuilder' => $baseDir . '/../lib/IconBuilder.php',
     'OCA\\Theming\\ImageManager' => $baseDir . '/../lib/ImageManager.php',
     'OCA\\Theming\\Jobs\\MigrateBackgroundImages' => $baseDir . '/../lib/Jobs/MigrateBackgroundImages.php',
+    'OCA\\Theming\\Jobs\\RestoreBackgroundImageColor' => $baseDir . '/../lib/Jobs/RestoreBackgroundImageColor.php',
     'OCA\\Theming\\Listener\\BeforePreferenceListener' => $baseDir . '/../lib/Listener/BeforePreferenceListener.php',
     'OCA\\Theming\\Listener\\BeforeTemplateRenderedListener' => $baseDir . '/../lib/Listener/BeforeTemplateRenderedListener.php',
     'OCA\\Theming\\Migration\\InitBackgroundImagesMigration' => $baseDir . '/../lib/Migration/InitBackgroundImagesMigration.php',
+    'OCA\\Theming\\Migration\\Version2006Date20240905111627' => $baseDir . '/../lib/Migration/Version2006Date20240905111627.php',
     'OCA\\Theming\\ResponseDefinitions' => $baseDir . '/../lib/ResponseDefinitions.php',
     'OCA\\Theming\\Service\\BackgroundService' => $baseDir . '/../lib/Service/BackgroundService.php',
     'OCA\\Theming\\Service\\JSDataService' => $baseDir . '/../lib/Service/JSDataService.php',
diff --git a/apps/theming/composer/composer/autoload_static.php b/apps/theming/composer/composer/autoload_static.php
index 17b195827f970..184d9ed07615b 100644
--- a/apps/theming/composer/composer/autoload_static.php
+++ b/apps/theming/composer/composer/autoload_static.php
@@ -32,9 +32,11 @@ class ComposerStaticInitTheming
         'OCA\\Theming\\IconBuilder' => __DIR__ . '/..' . '/../lib/IconBuilder.php',
         'OCA\\Theming\\ImageManager' => __DIR__ . '/..' . '/../lib/ImageManager.php',
         'OCA\\Theming\\Jobs\\MigrateBackgroundImages' => __DIR__ . '/..' . '/../lib/Jobs/MigrateBackgroundImages.php',
+        'OCA\\Theming\\Jobs\\RestoreBackgroundImageColor' => __DIR__ . '/..' . '/../lib/Jobs/RestoreBackgroundImageColor.php',
         'OCA\\Theming\\Listener\\BeforePreferenceListener' => __DIR__ . '/..' . '/../lib/Listener/BeforePreferenceListener.php',
         'OCA\\Theming\\Listener\\BeforeTemplateRenderedListener' => __DIR__ . '/..' . '/../lib/Listener/BeforeTemplateRenderedListener.php',
         'OCA\\Theming\\Migration\\InitBackgroundImagesMigration' => __DIR__ . '/..' . '/../lib/Migration/InitBackgroundImagesMigration.php',
+        'OCA\\Theming\\Migration\\Version2006Date20240905111627' => __DIR__ . '/..' . '/../lib/Migration/Version2006Date20240905111627.php',
         'OCA\\Theming\\ResponseDefinitions' => __DIR__ . '/..' . '/../lib/ResponseDefinitions.php',
         'OCA\\Theming\\Service\\BackgroundService' => __DIR__ . '/..' . '/../lib/Service/BackgroundService.php',
         'OCA\\Theming\\Service\\JSDataService' => __DIR__ . '/..' . '/../lib/Service/JSDataService.php',
diff --git a/apps/theming/lib/Controller/ThemingController.php b/apps/theming/lib/Controller/ThemingController.php
index 73ef78c7a8e8c..d6c89990b0284 100644
--- a/apps/theming/lib/Controller/ThemingController.php
+++ b/apps/theming/lib/Controller/ThemingController.php
@@ -22,6 +22,7 @@
 use OCP\AppFramework\Http\FileDisplayResponse;
 use OCP\AppFramework\Http\JSONResponse;
 use OCP\AppFramework\Http\NotFoundResponse;
+use OCP\AppFramework\Services\IAppConfig;
 use OCP\Files\NotFoundException;
 use OCP\Files\NotPermittedException;
 use OCP\IConfig;
@@ -40,34 +41,19 @@
 class ThemingController extends Controller {
 	public const VALID_UPLOAD_KEYS = ['header', 'logo', 'logoheader', 'background', 'favicon'];
 
-	private ThemingDefaults $themingDefaults;
-	private IL10N $l10n;
-	private IConfig $config;
-	private IURLGenerator $urlGenerator;
-	private IAppManager $appManager;
-	private ImageManager $imageManager;
-	private ThemesService $themesService;
-
 	public function __construct(
 		$appName,
 		IRequest $request,
-		IConfig $config,
-		ThemingDefaults $themingDefaults,
-		IL10N $l,
-		IURLGenerator $urlGenerator,
-		IAppManager $appManager,
-		ImageManager $imageManager,
-		ThemesService $themesService
+		private IConfig $config,
+		private IAppConfig $appConfig,
+		private ThemingDefaults $themingDefaults,
+		private IL10N $l10n,
+		private IURLGenerator $urlGenerator,
+		private IAppManager $appManager,
+		private ImageManager $imageManager,
+		private ThemesService $themesService,
 	) {
 		parent::__construct($appName, $request);
-
-		$this->themingDefaults = $themingDefaults;
-		$this->l10n = $l;
-		$this->config = $config;
-		$this->urlGenerator = $urlGenerator;
-		$this->appManager = $appManager;
-		$this->imageManager = $imageManager;
-		$this->themesService = $themesService;
 	}
 
 	/**
@@ -80,6 +66,7 @@ public function __construct(
 	public function updateStylesheet($setting, $value) {
 		$value = trim($value);
 		$error = null;
+		$saved = false;
 		switch ($setting) {
 			case 'name':
 				if (strlen($value) > 250) {
@@ -118,16 +105,25 @@ public function updateStylesheet($setting, $value) {
 			case 'primary_color':
 				if (!preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $value)) {
 					$error = $this->l10n->t('The given color is invalid');
+				} else {
+					$this->appConfig->setAppValueString('primary_color', $value);
+					$saved = true;
 				}
 				break;
 			case 'background_color':
 				if (!preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $value)) {
 					$error = $this->l10n->t('The given color is invalid');
+				} else {
+					$this->appConfig->setAppValueString('background_color', $value);
+					$saved = true;
 				}
 				break;
 			case 'disable-user-theming':
-				if ($value !== 'yes' && $value !== 'no') {
+				if (!in_array($value, ['yes', 'true', 'no', 'false'])) {
 					$error = $this->l10n->t('Disable-user-theming should be true or false');
+				} else {
+					$this->appConfig->setAppValueBool('disable-user-theming', $value === 'yes' || $value === 'true');
+					$saved = true;
 				}
 				break;
 		}
@@ -140,7 +136,9 @@ public function updateStylesheet($setting, $value) {
 			], Http::STATUS_BAD_REQUEST);
 		}
 
-		$this->themingDefaults->set($setting, $value);
+		if (!$saved) {
+			$this->themingDefaults->set($setting, $value);
+		}
 
 		return new DataResponse([
 			'data' => [
diff --git a/apps/theming/lib/Jobs/RestoreBackgroundImageColor.php b/apps/theming/lib/Jobs/RestoreBackgroundImageColor.php
new file mode 100644
index 0000000000000..1ec659d0646df
--- /dev/null
+++ b/apps/theming/lib/Jobs/RestoreBackgroundImageColor.php
@@ -0,0 +1,205 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Theming\Jobs;
+
+use OCA\Theming\AppInfo\Application;
+use OCA\Theming\Service\BackgroundService;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\BackgroundJob\IJobList;
+use OCP\BackgroundJob\QueuedJob;
+use OCP\Files\IAppData;
+use OCP\Files\NotFoundException;
+use OCP\Files\NotPermittedException;
+use OCP\IConfig;
+use OCP\IDBConnection;
+use Psr\Log\LoggerInterface;
+
+class RestoreBackgroundImageColor extends QueuedJob {
+
+	public const STAGE_PREPARE = 'prepare';
+	public const STAGE_EXECUTE = 'execute';
+	// will be saved in appdata/theming/global/
+	protected const STATE_FILE_NAME = '30_background_image_color_restoration.json';
+
+	public function __construct(
+		ITimeFactory $time,
+		private IConfig $config,
+		private IAppData $appData,
+		private IJobList $jobList,
+		private IDBConnection $dbc,
+		private LoggerInterface $logger,
+		private BackgroundService $service,
+	) {
+		parent::__construct($time);
+	}
+
+	protected function run(mixed $argument): void {
+		if (!is_array($argument) || !isset($argument['stage'])) {
+			throw new \Exception('Job '.self::class.' called with wrong argument');
+		}
+
+		switch ($argument['stage']) {
+			case self::STAGE_PREPARE:
+				$this->runPreparation();
+				break;
+			case self::STAGE_EXECUTE:
+				$this->runMigration();
+				break;
+			default:
+				break;
+		}
+	}
+
+	protected function runPreparation(): void {
+		try {
+			$qb = $this->dbc->getQueryBuilder();
+			$qb2 = $this->dbc->getQueryBuilder();
+
+			$innerSQL = $qb2->select('userid')
+				->from('preferences')
+				->where($qb2->expr()->eq('configkey', $qb->createNamedParameter('background_color')));
+
+			// Get those users, that have a background_image set - not the default, but no background_color.
+			$result = $qb->selectDistinct('a.userid')
+				->from('preferences', 'a')
+				->leftJoin('a', $qb->createFunction('('.$innerSQL->getSQL().')'), 'b', 'a.userid = b.userid')
+				->where($qb2->expr()->eq('a.configkey', $qb->createNamedParameter('background_image')))
+				->andWhere($qb2->expr()->neq('a.configvalue', $qb->createNamedParameter(BackgroundService::BACKGROUND_DEFAULT)))
+				->andWhere($qb2->expr()->isNull('b.userid'))
+				->executeQuery();
+
+			$userIds = $result->fetchAll(\PDO::FETCH_COLUMN);
+			$this->logger->info('Prepare to restore background information for {users} users', ['users' => count($userIds)]);
+			$this->storeUserIdsToProcess($userIds);
+		} catch (\Throwable $t) {
+			$this->jobList->add(self::class, ['stage' => self::STAGE_PREPARE]);
+			throw $t;
+		}
+		$this->jobList->add(self::class, ['stage' => self::STAGE_EXECUTE]);
+	}
+
+	/**
+	 * @throws NotPermittedException
+	 * @throws NotFoundException
+	 */
+	protected function runMigration(): void {
+		$allUserIds = $this->readUserIdsToProcess();
+		$notSoFastMode = count($allUserIds) > 1000;
+
+		$userIds = array_slice($allUserIds, 0, 1000);
+		foreach ($userIds as $userId) {
+			$backgroundColor = $this->config->getUserValue($userId, Application::APP_ID, 'background_color');
+			if ($backgroundColor !== '') {
+				continue;
+			}
+
+			$background = $this->config->getUserValue($userId, Application::APP_ID, 'background_image');
+			switch($background) {
+				case BackgroundService::BACKGROUND_DEFAULT:
+					$this->service->setDefaultBackground($userId);
+					break;
+				case BackgroundService::BACKGROUND_COLOR:
+					break;
+				case BackgroundService::BACKGROUND_CUSTOM:
+					$this->service->recalculateMeanColor($userId);
+					break;
+				default:
+					// shipped backgrounds
+					// do not alter primary color
+					$primary = $this->config->getUserValue($userId, Application::APP_ID, 'primary_color');
+					if (isset(BackgroundService::SHIPPED_BACKGROUNDS[$background])) {
+						$this->service->setShippedBackground($background, $userId);
+					} else {
+						$this->service->setDefaultBackground($userId);
+					}
+					// Restore primary
+					if ($primary !== '') {
+						$this->config->setUserValue($userId, Application::APP_ID, 'primary_color', $primary);
+					}
+			}
+		}
+
+		if ($notSoFastMode) {
+			$remainingUserIds = array_slice($allUserIds, 1000);
+			$this->storeUserIdsToProcess($remainingUserIds);
+			$this->jobList->add(self::class, ['stage' => self::STAGE_EXECUTE]);
+		} else {
+			$this->deleteStateFile();
+		}
+	}
+
+	/**
+	 * @throws NotPermittedException
+	 * @throws NotFoundException
+	 */
+	protected function readUserIdsToProcess(): array {
+		$globalFolder = $this->appData->getFolder('global');
+		if ($globalFolder->fileExists(self::STATE_FILE_NAME)) {
+			$file = $globalFolder->getFile(self::STATE_FILE_NAME);
+			try {
+				$userIds = \json_decode($file->getContent(), true);
+			} catch (NotFoundException $e) {
+				$userIds = [];
+			}
+			if ($userIds === null) {
+				$userIds = [];
+			}
+		} else {
+			$userIds = [];
+		}
+		return $userIds;
+	}
+
+	/**
+	 * @throws NotFoundException
+	 */
+	protected function storeUserIdsToProcess(array $userIds): void {
+		$storableUserIds = \json_encode($userIds);
+		$globalFolder = $this->appData->getFolder('global');
+		try {
+			if ($globalFolder->fileExists(self::STATE_FILE_NAME)) {
+				$file = $globalFolder->getFile(self::STATE_FILE_NAME);
+			} else {
+				$file = $globalFolder->newFile(self::STATE_FILE_NAME);
+			}
+			$file->putContent($storableUserIds);
+		} catch (NotFoundException $e) {
+		} catch (NotPermittedException $e) {
+			$this->logger->warning('Lacking permissions to create {file}',
+				[
+					'app' => 'theming',
+					'file' => self::STATE_FILE_NAME,
+					'exception' => $e,
+				]
+			);
+		}
+	}
+
+	/**
+	 * @throws NotFoundException
+	 */
+	protected function deleteStateFile(): void {
+		$globalFolder = $this->appData->getFolder('global');
+		if ($globalFolder->fileExists(self::STATE_FILE_NAME)) {
+			$file = $globalFolder->getFile(self::STATE_FILE_NAME);
+			try {
+				$file->delete();
+			} catch (NotPermittedException $e) {
+				$this->logger->info('Could not delete {file} due to permissions. It is safe to delete manually inside data -> appdata -> theming -> global.',
+					[
+						'app' => 'theming',
+						'file' => $file->getName(),
+						'exception' => $e,
+					]
+				);
+			}
+		}
+	}
+}
diff --git a/apps/theming/lib/Migration/Version2006Date20240905111627.php b/apps/theming/lib/Migration/Version2006Date20240905111627.php
new file mode 100644
index 0000000000000..dcec954f585a0
--- /dev/null
+++ b/apps/theming/lib/Migration/Version2006Date20240905111627.php
@@ -0,0 +1,88 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Theming\Migration;
+
+use Closure;
+use OCA\Theming\AppInfo\Application;
+use OCA\Theming\Jobs\RestoreBackgroundImageColor;
+use OCP\BackgroundJob\IJobList;
+use OCP\IAppConfig;
+use OCP\IDBConnection;
+use OCP\Migration\IOutput;
+
+// This can only be executed once because `background_color` is again used with Nextcloud 30,
+// so this part only works when updating -> Nextcloud 29 -> 30
+class Version2006Date20240905111627 implements \OCP\Migration\IMigrationStep {
+
+	public function __construct(
+		private IJobList $jobList,
+		private IAppConfig $appConfig,
+		private IDBConnection $connection,
+	) {
+	}
+
+	public function name(): string {
+		return 'Restore custom primary color';
+	}
+
+	public function description(): string {
+		return 'Restore custom primary color after separating primary color from background color';
+	}
+
+	public function preSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
+		// nop
+	}
+
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options) {
+		$this->restoreSystemColors($output);
+
+		$userThemingEnabled = $this->appConfig->getValueBool('theming', 'disable-user-theming') === false;
+		if ($userThemingEnabled) {
+			$this->restoreUserColors($output);
+		}
+
+		return null;
+	}
+
+	public function postSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
+		$output->info('Initialize restoring of background colors for custom background images');
+		// This is done in a background job as this can take a lot of time for large instances
+		$this->jobList->add(RestoreBackgroundImageColor::class, ['stage' => RestoreBackgroundImageColor::STAGE_PREPARE]);
+	}
+
+	private function restoreSystemColors(IOutput $output): void {
+		$defaultColor = $this->appConfig->getValueString(Application::APP_ID, 'color', '');
+		if ($defaultColor === '') {
+			$output->info('No custom system color configured - skipping');
+		} else {
+			// Restore legacy value into new field
+			$this->appConfig->setValueString(Application::APP_ID, 'background_color', $defaultColor);
+			$this->appConfig->setValueString(Application::APP_ID, 'primary_color', $defaultColor);
+			// Delete legacy field
+			$this->appConfig->deleteKey(Application::APP_ID, 'color');
+			// give some feedback
+			$output->info('Global primary color restored');
+		}
+	}
+
+	private function restoreUserColors(IOutput $output): void {
+		$output->info('Restoring user primary color');
+		// For performance let the DB handle this
+		$qb = $this->connection->getQueryBuilder();
+		// Rename the `background_color` config to `primary_color` as this was the behavior on Nextcloud 29 and older
+		// with Nextcloud 30 `background_color` is a new option to define the background color independent of the primary color.
+		$qb->update('preferences')
+			->set('configkey', $qb->createNamedParameter('primary_color'))
+			->where($qb->expr()->eq('appid', $qb->createNamedParameter(Application::APP_ID)))
+			->andWhere($qb->expr()->eq('configkey', $qb->createNamedParameter('background_color')));
+		$qb->executeStatement();
+		$output->info('Primary color of users restored');
+	}
+}
diff --git a/apps/theming/lib/Service/BackgroundService.php b/apps/theming/lib/Service/BackgroundService.php
index bd87bc1aa21b0..6cb2b4abeb9df 100644
--- a/apps/theming/lib/Service/BackgroundService.php
+++ b/apps/theming/lib/Service/BackgroundService.php
@@ -205,10 +205,15 @@ public function __construct(
 	) {
 	}
 
-	public function setDefaultBackground(): void {
-		$this->config->deleteUserValue($this->userId, Application::APP_ID, 'background_image');
-		$this->config->deleteUserValue($this->userId, Application::APP_ID, 'background_color');
-		$this->config->deleteUserValue($this->userId, Application::APP_ID, 'primary_color');
+	public function setDefaultBackground(?string $userId = null): void {
+		$userId = $userId ?? $this->userId;
+		if ($userId === null) {
+			throw new RuntimeException('No currently logged-in user');
+		}
+
+		$this->config->deleteUserValue($userId, Application::APP_ID, 'background_image');
+		$this->config->deleteUserValue($userId, Application::APP_ID, 'background_color');
+		$this->config->deleteUserValue($userId, Application::APP_ID, 'primary_color');
 	}
 
 	/**
@@ -227,9 +232,24 @@ public function setFileBackground($path): void {
 
 		/** @var File $file */
 		$file = $userFolder->get($path);
-		$image = new \OCP\Image();
+		$handle = $file->fopen('r');
+		if ($handle === false) {
+			throw new InvalidArgumentException('Invalid image file');
+		}
+		$this->getAppDataFolder()->newFile('background.jpg', $handle);
+
+		$this->recalculateMeanColor();
+	}
+
+	public function recalculateMeanColor(?string $userId = null): void {
+		$userId = $userId ?? $this->userId;
+		if ($userId === null) {
+			throw new RuntimeException('No currently logged-in user');
+		}
 
-		if ($image->loadFromFileHandle($file->fopen('r')) === false) {
+		$image = new \OCP\Image();
+		$handle = $this->getAppDataFolder($userId)->getFile('background.jpg')->read();
+		if ($handle === false || $image->loadFromFileHandle($handle) === false) {
 			throw new InvalidArgumentException('Invalid image file');
 		}
 
@@ -237,35 +257,43 @@ public function setFileBackground($path): void {
 		if ($meanColor !== false) {
 			$this->setColorBackground($meanColor);
 		}
-
-		$this->getAppDataFolder()->newFile('background.jpg', $file->fopen('r'));
-		$this->config->setUserValue($this->userId, Application::APP_ID, 'background_image', self::BACKGROUND_CUSTOM);
+		$this->config->setUserValue($userId, Application::APP_ID, 'background_image', self::BACKGROUND_CUSTOM);
 	}
 
-	public function setShippedBackground($fileName): void {
-		if ($this->userId === null) {
+	/**
+	 * Set background of user to a shipped background identified by the filename
+	 * @param string $filename The shipped background filename
+	 * @param null|string $userId The user to set - defaults to currently logged in user
+	 * @throws RuntimeException If neither $userId is specified nor a user is logged in
+	 * @throws InvalidArgumentException If the specified filename does not match any shipped background
+	 */
+	public function setShippedBackground(string $filename, ?string $userId = null): void {
+		$userId = $userId ?? $this->userId;
+		if ($userId === null) {
 			throw new RuntimeException('No currently logged-in user');
 		}
-		if (!array_key_exists($fileName, self::SHIPPED_BACKGROUNDS)) {
+		if (!array_key_exists($filename, self::SHIPPED_BACKGROUNDS)) {
 			throw new InvalidArgumentException('The given file name is invalid');
 		}
-		$this->setColorBackground(self::SHIPPED_BACKGROUNDS[$fileName]['background_color']);
-		$this->config->setUserValue($this->userId, Application::APP_ID, 'background_image', $fileName);
-		$this->config->setUserValue($this->userId, Application::APP_ID, 'primary_color', self::SHIPPED_BACKGROUNDS[$fileName]['primary_color']);
+		$this->setColorBackground(self::SHIPPED_BACKGROUNDS[$filename]['background_color'], $userId);
+		$this->config->setUserValue($userId, Application::APP_ID, 'background_image', $filename);
+		$this->config->setUserValue($userId, Application::APP_ID, 'primary_color', self::SHIPPED_BACKGROUNDS[$filename]['primary_color']);
 	}
 
 	/**
 	 * Set the background to color only
+	 * @param string|null $userId The user to set the color - default to current logged-in user
 	 */
-	public function setColorBackground(string $color): void {
-		if ($this->userId === null) {
+	public function setColorBackground(string $color, ?string $userId = null): void {
+		$userId = $userId ?? $this->userId;
+		if ($userId === null) {
 			throw new RuntimeException('No currently logged-in user');
 		}
 		if (!preg_match('/^#([0-9a-f]{3}|[0-9a-f]{6})$/i', $color)) {
 			throw new InvalidArgumentException('The given color is invalid');
 		}
-		$this->config->setUserValue($this->userId, Application::APP_ID, 'background_color', $color);
-		$this->config->setUserValue($this->userId, Application::APP_ID, 'background_image', self::BACKGROUND_COLOR);
+		$this->config->setUserValue($userId, Application::APP_ID, 'background_color', $color);
+		$this->config->setUserValue($userId, Application::APP_ID, 'background_image', self::BACKGROUND_COLOR);
 	}
 
 	public function deleteBackgroundImage(): void {
@@ -366,19 +394,24 @@ function toHex(int $channel): string {
 	/**
 	 * Storing the data in appdata/theming/users/USERID
 	 *
-	 * @return ISimpleFolder
+	 * @param string|null $userId The user to get the folder - default to current user
 	 * @throws NotPermittedException
 	 */
-	private function getAppDataFolder(): ISimpleFolder {
+	private function getAppDataFolder(?string $userId = null): ISimpleFolder {
+		$userId = $userId ?? $this->userId;
+		if ($userId === null) {
+			throw new RuntimeException('No currently logged-in user');
+		}
+
 		try {
 			$rootFolder = $this->appData->getFolder('users');
 		} catch (NotFoundException $e) {
 			$rootFolder = $this->appData->newFolder('users');
 		}
 		try {
-			return $rootFolder->getFolder($this->userId);
+			return $rootFolder->getFolder($userId);
 		} catch (NotFoundException $e) {
-			return $rootFolder->newFolder($this->userId);
+			return $rootFolder->newFolder($userId);
 		}
 	}
 }
diff --git a/apps/theming/lib/ThemingDefaults.php b/apps/theming/lib/ThemingDefaults.php
index f43e96a883051..9be830a61fda9 100644
--- a/apps/theming/lib/ThemingDefaults.php
+++ b/apps/theming/lib/ThemingDefaults.php
@@ -11,6 +11,7 @@
 use OCP\App\IAppManager;
 use OCP\Files\NotFoundException;
 use OCP\Files\SimpleFS\ISimpleFile;
+use OCP\IAppConfig;
 use OCP\ICacheFactory;
 use OCP\IConfig;
 use OCP\IL10N;
@@ -39,6 +40,7 @@ class ThemingDefaults extends \OC_Defaults {
 	 */
 	public function __construct(
 		private IConfig $config,
+		private IAppConfig $appConfig,
 		private IL10N $l,
 		private IUserSession $userSession,
 		private IURLGenerator $urlGenerator,
@@ -206,9 +208,9 @@ public function getColorBackground(): string {
 
 		// user-defined background color
 		if (!empty($user)) {
-			$userPrimaryColor = $this->config->getUserValue($user->getUID(), Application::APP_ID, 'background_color', '');
-			if (preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $userPrimaryColor)) {
-				return $userPrimaryColor;
+			$userBackgroundColor = $this->config->getUserValue($user->getUID(), Application::APP_ID, 'background_color', '');
+			if (preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $userBackgroundColor)) {
+				return $userBackgroundColor;
 			}
 		}
 
@@ -221,7 +223,7 @@ public function getColorBackground(): string {
 	 */
 	public function getDefaultColorPrimary(): string {
 		// try admin color
-		$defaultColor = $this->config->getAppValue(Application::APP_ID, 'primary_color', '');
+		$defaultColor = $this->appConfig->getValueString(Application::APP_ID, 'primary_color', '');
 		if (preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $defaultColor)) {
 			return $defaultColor;
 		}
@@ -234,7 +236,7 @@ public function getDefaultColorPrimary(): string {
 	 * Default background color only taking admin setting into account
 	 */
 	public function getDefaultColorBackground(): string {
-		$defaultColor = $this->config->getAppValue(Application::APP_ID, 'background_color', '');
+		$defaultColor = $this->appConfig->getValueString(Application::APP_ID, 'background_color');
 		if (preg_match('/^\#([0-9a-f]{3}|[0-9a-f]{6})$/i', $defaultColor)) {
 			return $defaultColor;
 		}
@@ -344,7 +346,7 @@ public function getScssVariables() {
 		$variables['image-login-background'] = "url('".$this->imageManager->getImageUrl('background')."')";
 		$variables['image-login-plain'] = 'false';
 
-		if ($this->config->getAppValue('theming', 'primary_color', '') !== '') {
+		if ($this->appConfig->getValueString(Application::APP_ID, 'primary_color', '') !== '') {
 			$variables['color-primary'] = $this->getColorPrimary();
 			$variables['color-primary-text'] = $this->getTextColorPrimary();
 			$variables['color-primary-element'] = $this->util->elementColor($this->getColorPrimary());
@@ -520,6 +522,6 @@ public function getDefaultTextColorPrimary() {
 	 * Has the admin disabled user customization
 	 */
 	public function isUserThemingDisabled(): bool {
-		return $this->config->getAppValue('theming', 'disable-user-theming', 'no') === 'yes';
+		return $this->appConfig->getValueBool(Application::APP_ID, 'disable-user-theming');
 	}
 }
diff --git a/apps/theming/tests/Controller/ThemingControllerTest.php b/apps/theming/tests/Controller/ThemingControllerTest.php
index 86231e7daf7ec..280bb8df4d173 100644
--- a/apps/theming/tests/Controller/ThemingControllerTest.php
+++ b/apps/theming/tests/Controller/ThemingControllerTest.php
@@ -13,6 +13,7 @@
 use OCP\App\IAppManager;
 use OCP\AppFramework\Http;
 use OCP\AppFramework\Http\DataResponse;
+use OCP\AppFramework\Services\IAppConfig;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\Files\NotFoundException;
 use OCP\Files\SimpleFS\ISimpleFile;
@@ -24,28 +25,23 @@
 use Test\TestCase;
 
 class ThemingControllerTest extends TestCase {
-	/** @var IRequest|MockObject */
-	private $request;
-	/** @var IConfig|MockObject */
-	private $config;
-	/** @var ThemingDefaults|MockObject */
-	private $themingDefaults;
-	/** @var IL10N|MockObject */
-	private $l10n;
-	/** @var ThemingController */
-	private $themingController;
-	/** @var IAppManager|MockObject */
-	private $appManager;
-	/** @var ImageManager|MockObject */
-	private $imageManager;
-	/** @var IURLGenerator|MockObject */
-	private $urlGenerator;
-	/** @var ThemesService|MockObject */
-	private $themesService;
+
+	private IRequest&MockObject $request;
+	private IConfig&MockObject $config;
+	private IAppConfig&MockObject $appConfig;
+	private ThemingDefaults&MockObject $themingDefaults;
+	private IL10N&MockObject $l10n;
+	private IAppManager&MockObject $appManager;
+	private ImageManager&MockObject $imageManager;
+	private IURLGenerator&MockObject $urlGenerator;
+	private ThemesService&MockObject $themesService;
+
+	private ThemingController $themingController;
 
 	protected function setUp(): void {
 		$this->request = $this->createMock(IRequest::class);
 		$this->config = $this->createMock(IConfig::class);
+		$this->appConfig = $this->createMock(IAppConfig::class);
 		$this->themingDefaults = $this->createMock(ThemingDefaults::class);
 		$this->l10n = $this->createMock(L10N::class);
 		$this->appManager = $this->createMock(IAppManager::class);
@@ -64,6 +60,7 @@ protected function setUp(): void {
 			'theming',
 			$this->request,
 			$this->config,
+			$this->appConfig,
 			$this->themingDefaults,
 			$this->l10n,
 			$this->urlGenerator,
diff --git a/apps/theming/tests/ThemingDefaultsTest.php b/apps/theming/tests/ThemingDefaultsTest.php
index 0dbf4336e8ae3..8edbcbc53c1b5 100644
--- a/apps/theming/tests/ThemingDefaultsTest.php
+++ b/apps/theming/tests/ThemingDefaultsTest.php
@@ -10,8 +10,8 @@
 use OCA\Theming\ThemingDefaults;
 use OCA\Theming\Util;
 use OCP\App\IAppManager;
-use OCP\Files\IAppData;
 use OCP\Files\NotFoundException;
+use OCP\IAppConfig;
 use OCP\ICache;
 use OCP\ICacheFactory;
 use OCP\IConfig;
@@ -20,21 +20,20 @@
 use OCP\IURLGenerator;
 use OCP\IUser;
 use OCP\IUserSession;
+use PHPUnit\Framework\MockObject\MockObject;
 use Test\TestCase;
 
 class ThemingDefaultsTest extends TestCase {
-	/** @var IConfig|\PHPUnit\Framework\MockObject\MockObject */
-	private $config;
+	private IAppConfig&MockObject $appConfig;
+	private IConfig&MockObject $config;
+	private \OC_Defaults $defaults;
+
 	/** @var IL10N|\PHPUnit\Framework\MockObject\MockObject */
 	private $l10n;
 	/** @var IUserSession|\PHPUnit\Framework\MockObject\MockObject */
 	private $userSession;
 	/** @var IURLGenerator|\PHPUnit\Framework\MockObject\MockObject */
 	private $urlGenerator;
-	/** @var \OC_Defaults|\PHPUnit\Framework\MockObject\MockObject */
-	private $defaults;
-	/** @var IAppData|\PHPUnit\Framework\MockObject\MockObject */
-	private $appData;
 	/** @var ICacheFactory|\PHPUnit\Framework\MockObject\MockObject */
 	private $cacheFactory;
 	/** @var ThemingDefaults */
@@ -54,6 +53,7 @@ class ThemingDefaultsTest extends TestCase {
 
 	protected function setUp(): void {
 		parent::setUp();
+		$this->appConfig = $this->createMock(IAppConfig::class);
 		$this->config = $this->createMock(IConfig::class);
 		$this->l10n = $this->createMock(IL10N::class);
 		$this->userSession = $this->createMock(IUserSession::class);
@@ -72,6 +72,7 @@ protected function setUp(): void {
 			->willReturn('');
 		$this->template = new ThemingDefaults(
 			$this->config,
+			$this->appConfig,
 			$this->l10n,
 			$this->userSession,
 			$this->urlGenerator,
@@ -398,25 +399,31 @@ public function testGetShortFooterInvalidPrivacy($invalidPrivacyUrl) {
 	}
 
 	public function testGetColorPrimaryWithDefault() {
-		$this->config
-			->expects($this->exactly(2))
-			->method('getAppValue')
-			->willReturnMap([
-				['theming', 'disable-user-theming', 'no', 'no'],
-				['theming', 'primary_color', '', $this->defaults->getColorPrimary()],
-			]);
+		$this->appConfig
+			->expects(self::once())
+			->method('getValueBool')
+			->with('theming', 'disable-user-theming')
+			->willReturn(false);
+		$this->appConfig
+			->expects(self::once())
+			->method('getValueString')
+			->with('theming', 'primary_color', '')
+			->willReturn($this->defaults->getColorPrimary());
 
 		$this->assertEquals($this->defaults->getColorPrimary(), $this->template->getColorPrimary());
 	}
 
 	public function testGetColorPrimaryWithCustom() {
-		$this->config
-			->expects($this->exactly(2))
-			->method('getAppValue')
-			->willReturnMap([
-				['theming', 'disable-user-theming', 'no', 'no'],
-				['theming', 'primary_color', '', '#fff'],
-			]);
+		$this->appConfig
+			->expects(self::once())
+			->method('getValueBool')
+			->with('theming', 'disable-user-theming')
+			->willReturn(false);
+		$this->appConfig
+			->expects(self::once())
+			->method('getValueString')
+			->with('theming', 'primary_color', '')
+			->willReturn('#fff');
 
 		$this->assertEquals('#fff', $this->template->getColorPrimary());
 	}
@@ -424,37 +431,37 @@ public function testGetColorPrimaryWithCustom() {
 	public function dataGetColorPrimary() {
 		return [
 			'with fallback default' => [
-				'disableTheming' => 'no',
+				'disableTheming' => false,
 				'primaryColor' => '',
 				'userPrimaryColor' => '',
 				'expected' => BackgroundService::DEFAULT_COLOR,
 			],
 			'with custom admin primary' => [
-				'disableTheming' => 'no',
+				'disableTheming' => false,
 				'primaryColor' => '#aaa',
 				'userPrimaryColor' => '',
 				'expected' => '#aaa',
 			],
 			'with custom invalid admin primary' => [
-				'disableTheming' => 'no',
+				'disableTheming' => false,
 				'primaryColor' => 'invalid',
 				'userPrimaryColor' => '',
 				'expected' => BackgroundService::DEFAULT_COLOR,
 			],
 			'with custom invalid user primary' => [
-				'disableTheming' => 'no',
+				'disableTheming' => false,
 				'primaryColor' => '',
 				'userPrimaryColor' => 'invalid-name',
 				'expected' => BackgroundService::DEFAULT_COLOR,
 			],
 			'with custom user primary' => [
-				'disableTheming' => 'no',
+				'disableTheming' => false,
 				'primaryColor' => '',
 				'userPrimaryColor' => '#bbb',
 				'expected' => '#bbb',
 			],
 			'with disabled user theming primary' => [
-				'disableTheming' => 'yes',
+				'disableTheming' => true,
 				'primaryColor' => '#aaa',
 				'userPrimaryColor' => '#bbb',
 				'expected' => '#aaa',
@@ -465,7 +472,7 @@ public function dataGetColorPrimary() {
 	/**
 	 * @dataProvider dataGetColorPrimary
 	 */
-	public function testGetColorPrimary(string $disableTheming, string $primaryColor, string $userPrimaryColor, string $expected) {
+	public function testGetColorPrimary(bool $disableTheming, string $primaryColor, string $userPrimaryColor, string $expected) {
 		$user = $this->createMock(IUser::class);
 		$this->userSession->expects($this->any())
 			->method('getUser')
@@ -473,13 +480,16 @@ public function testGetColorPrimary(string $disableTheming, string $primaryColor
 		$user->expects($this->any())
 			->method('getUID')
 			->willReturn('user');
-		$this->config
-			->expects($this->any())
-			->method('getAppValue')
-			->willReturnMap([
-				['theming', 'disable-user-theming', 'no', $disableTheming],
-				['theming', 'primary_color', '', $primaryColor],
-			]);
+		$this->appConfig
+			->expects(self::any())
+			->method('getValueBool')
+			->with('theming', 'disable-user-theming')
+			->willReturn($disableTheming);
+		$this->appConfig
+			->expects(self::any())
+			->method('getValueString')
+			->with('theming', 'primary_color', '')
+			->willReturn($primaryColor);
 		$this->config
 			->expects($this->any())
 			->method('getUserValue')
@@ -699,8 +709,14 @@ public function testGetScssVariables() {
 				['theming', 'backgroundMime', '', 'jpeg'],
 				['theming', 'logoheaderMime', '', 'jpeg'],
 				['theming', 'faviconMime', '', 'jpeg'],
-				['theming', 'primary_color', '', $this->defaults->getColorPrimary()],
-				['theming', 'primary_color', $this->defaults->getColorPrimary(), $this->defaults->getColorPrimary()],
+			]);
+		
+		$this->appConfig
+			->expects(self::atLeastOnce())
+			->method('getValueString')
+			->willReturnMap([
+				['theming', 'primary_color', '', false, $this->defaults->getColorPrimary()],
+				['theming', 'primary_color', $this->defaults->getColorPrimary(), false, $this->defaults->getColorPrimary()],
 			]);
 
 		$this->util->expects($this->any())->method('invertTextColor')->with($this->defaults->getColorPrimary())->willReturn(false);
diff --git a/lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php b/lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php
index 175b7c1a42eb7..9d351c1d3f17e 100644
--- a/lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php
+++ b/lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php
@@ -185,7 +185,7 @@ public function innerJoin($fromAlias, $join, $alias, $condition = null): self {
 	}
 
 	public function leftJoin($fromAlias, $join, $alias, $condition = null): self {
-		return $this->join($fromAlias, $join, $alias, $condition, PartitionQuery::JOIN_MODE_LEFT);
+		return $this->join($fromAlias, (string)$join, $alias, $condition, PartitionQuery::JOIN_MODE_LEFT);
 	}
 
 	public function join($fromAlias, $join, $alias, $condition = null, $joinMode = PartitionQuery::JOIN_MODE_INNER): self {
diff --git a/lib/private/DB/QueryBuilder/QueryBuilder.php b/lib/private/DB/QueryBuilder/QueryBuilder.php
index ec2581d7e9a8b..d1207ebdb97ad 100644
--- a/lib/private/DB/QueryBuilder/QueryBuilder.php
+++ b/lib/private/DB/QueryBuilder/QueryBuilder.php
@@ -764,7 +764,7 @@ public function innerJoin($fromAlias, $join, $alias, $condition = null) {
 	 * </code>
 	 *
 	 * @param string $fromAlias The alias that points to a from clause.
-	 * @param string $join The table name to join.
+	 * @param string|IQueryFunction $join The table name or sub-query to join.
 	 * @param string $alias The alias of the join table.
 	 * @param string|ICompositeExpression|null $condition The condition for the join.
 	 *
diff --git a/lib/private/Server.php b/lib/private/Server.php
index ae2355f40c0ee..a6f7cc61faa30 100644
--- a/lib/private/Server.php
+++ b/lib/private/Server.php
@@ -1167,6 +1167,7 @@ public function __construct($webRoot, \OC\Config $config) {
 				);
 				return new ThemingDefaults(
 					$c->get(\OCP\IConfig::class),
+					$c->get(\OCP\IAppConfig::class),
 					$c->getL10N('theming'),
 					$c->get(IUserSession::class),
 					$c->get(IURLGenerator::class),
diff --git a/lib/public/DB/QueryBuilder/IQueryBuilder.php b/lib/public/DB/QueryBuilder/IQueryBuilder.php
index b673c5ef6ec77..0c2aa4669c1ce 100644
--- a/lib/public/DB/QueryBuilder/IQueryBuilder.php
+++ b/lib/public/DB/QueryBuilder/IQueryBuilder.php
@@ -541,12 +541,13 @@ public function innerJoin($fromAlias, $join, $alias, $condition = null);
 	 * </code>
 	 *
 	 * @param string $fromAlias The alias that points to a from clause.
-	 * @param string $join The table name to join.
+	 * @param string|IQueryFunction $join The table name to join.
 	 * @param string $alias The alias of the join table.
 	 * @param string|ICompositeExpression|null $condition The condition for the join.
 	 *
 	 * @return $this This QueryBuilder instance.
 	 * @since 8.2.0
+	 * @since 30.0.0 Allow passing IQueryFunction as parameter for `$join` to allow join with a sub-query.
 	 *
 	 * @psalm-taint-sink sql $fromAlias
 	 * @psalm-taint-sink sql $join
@@ -1001,11 +1002,14 @@ public function createFunction($call);
 	public function getLastInsertId(): int;
 
 	/**
-	 * Returns the table name quoted and with database prefix as needed by the implementation
+	 * Returns the table name quoted and with database prefix as needed by the implementation.
+	 * If a query function is passed the function is casted to string,
+	 * this allows passing functions as sub-queries for join expression.
 	 *
 	 * @param string|IQueryFunction $table
 	 * @return string
 	 * @since 9.0.0
+	 * @since 24.0.0 accepts IQueryFunction as parameter
 	 */
 	public function getTableName($table);