Created attachment 178218 [details]
example of settings that will cause this problem

SUMMARY

In System Settings -> Input and Output -> Keyboard, if you set a non english layout which uses 3rd level, and then in configure key options set both a alt and win behavior, and a key to choose 3rd level (even if these behaviors should not be incompatible with each other). You will be able to use this third level in applications like Kate or Konsole but not applications like Firefox, or Libreoffice. I believe this is because they are GNOME applications as this happens in firefox which is running via Wayland.

Note that setting either Key to Choose 3rd Level OR Alt and Win Behaviors, does cause the behavior to work properly, but setting both causes the key you set to choose 3rd level to stop working.


STEPS TO REPRODUCE
1. Set your layout to a non english layout
2. go to key bindings, configure key options and enable any alt and win behavior that won't affect right alt
3. enable any key to choose the 3rd level that should not be incompatible with an alt and win behavior.

See screenshots for a combination of settings that causes this problem.

OBSERVED RESULT
In software like Kate you can type non english characters from the third level as expected for these settings. In software like Firefox, you will be unable to type any characters while pressing this third level button

EXPECTED RESULT
Typing in all programs should be the same.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Nobara - 6.12.11-204.nobara.fc41.x86_64
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.9.0
Qt Version: 6.8.1
Graphics Platform: Wayland

ADDITIONAL INFORMATION