SUMMARY
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I'm not sure if this is related to Krita or Plasmashell but here it is. There is no menu (file, edit, ...) when running Krita. I have tested with two global menu widgets (one the kde plasma official and one a third-party) and there was no menu in either of them. I tested with a new user and in-app menu was ok until I added a global menu widget. Then the in-app menu was gone and global menu didn't come. Running it through command line with the command:

KDE_NO_GLOBAL_MENU=0 krita

will launch it with in-app menus. I tested with X11 and Wayland and there was no difference. I tried removing ~/.config/kritarc and it had no effects. The global menu is OK in other apps.
 
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STEPS TO REPRODUCE
1. Install Krita
2. Have a Global Menu
3. Launch Krita

OBSERVED RESULT
No menu

EXPECTED RESULT
Showing menu in global menu widget

SOFTWARE/OS VERSIONS
Linux: 6.0.3-arch2-1 
(available in About System)
KDE Plasma Version: 5.26.1
KDE Frameworks Version: 5.99.0
Qt Version: 5.15.6
ADDITIONAL INFORMATION