Created attachment 151951 [details]
Minimal project to reproduce the bug

SUMMARY
When debugging a c/c++ project with gdb, if a break point is triggered in a specific way, cursor will stay hidden even if the window loses focus. This makes the user unable to use the mouse whenever a breakpoint is hit. Essentially making debugging apps in plasma DE a nightmare.

I believe this is a kwin issue because if I understand correctly, kwin doesn't let apps hide the cursor from all windows, just from the windows created from host app's process.
 
The function for hiding the cursor from GLFW is  
glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED); 

I tried producing a minimal example to reproduce the bug. It is a cmake project attached to this issue. It might need some tinkering to make it work on your setup, I'm using vs code, so I left the configuration files there in case it is useful for anyone.

STEPS TO REPRODUCE
1. Install GLFW3 and download attached project
2. Generate CMake project with "cmake -DCMAKE_BUILD_TYPE=Debug ."
3. Place breakpoint on line 18 (end bracket) on main.c
4. Start debugging and exit the app(Alt + F4 for me), without making the window lose focus
5. Break point is hit, app loses focus but cursor still doesn't show 

OBSERVED RESULT
Cursor is hidden even when focusing other apps

EXPECTED RESULT
Cursor should be visible (shouldn't it?)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Archlinux
KDE Plasma Version: 5.25.4
KDE Frameworks Version: 5.97.0
Qt Version: 5.15.5