[GUI][Processing] The "Selected features only" checkbox is incorrectly disabled / enabled although the layer has / has not selected features

[agiudiceandrea]

What is the bug or the crash?

In some circumstances, the "Selected features only" checkbox in the processing algorithms' GUI is disabled although the input layer has selected features or is enabled although the input layer has not selected features.

Video_2025-01-10_133511.mp4

Steps to reproduce the issue

1. in a new project add the "World Map" Easter-egg layer
2. create a "New scratch layer" point memory layer and add 1 point feature
3. ensure that the "New scratch layer" layer is the active layer and select the point feature in it
4. open any processing algorithm dialog window, e.g. the "Buffer" processing algorithm (the Input layer parameter is automatically set to the "New scratch layer" layer)
5. observe that the "Selected features only" checkbox is incorrectly disabled although it has a selected feature
6. close the processing algorithm dialog window
7. deselect the point feature in the "New scratch layer" layer
8. make the "World Map" layer the active layer and select a feature in it
9. make the "New scratch layer" layer the active layer and open any processing algorithm dialog window, e.g. the "Buffer" processing algorithm (the Input layer parameter is automatically set to the "New scratch layer" layer)
10. observe that the "Selected features only" checkbox is incorrectly enabled although it has not any selected feature

Versions

QGIS LTR 3.34.14 and QGIS 3.40.2 (OSGeo4W) on Windows

QGIS version	3.40.2-Bratislava
QGIS code revision	14826ca1
Libraries
Qt version	5.15.13
Python version	3.12.8
GDAL/OGR version	3.9.3
PROJ version	9.5.0
EPSG Registry database version	v11.016 (2024-08-31)
GEOS version	3.13.0-CAPI-1.19.0
SQLite version	3.46.1
PDAL version	2.8.1
PostgreSQL client version	16.2
SpatiaLite version	5.1.0
QWT version	6.3.0
QScintilla2 version	2.14.1
OS version	Windows 10 Version 1903
Active Python plugins
db_manager	0.1.20
grassprovider	2.12.99
MetaSearch	0.3.6
processing	2.12.99

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

The issue didn't occur running QGIS <= 3.22, while it occurs using QGIS >= 3.26.