STEPS TO REPRODUCE
1.  Open Krita appimage
2.  Drag at least 2 pictures in the window
3.  Make a selection on picture 1 and ctrl+c
4. Switch to picture 2 (ctrl tab, or use tabs to select another picture, or any other method work)
5. ctrl+v

OBSERVED RESULT
Krita crashes.

EXPECTED RESULT
Krita doesn't crash and the selection is pasted on a new layer.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 39
KDE Plasma Version: 5.27.11
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.14
Kernel Version: 6.9.12-100.fc39.x86_64 (64-bit)
Krita 5.2.3

ADDITIONAL INFORMATION
Tested on krita-5.2.2 and it doesn't crash.
Notice when switching between documents that no layer is selected in 5.2.3 (in 5.2.2, the background layer is selected by default). no layer operations (layer type, adding/deleting layers) can be done until you manually select one of the existing layers first.
100% Reproduce rate.