SUMMARY
When switching any application to fullscreen or switching focus back to any application that already is in fullscreen, everything freezes for two seconds and my built-in monitor turns black until I focus any application that is not in fullscreen. If the fullscreen application is on my build-in monitor, everything works as expected. This only happens if I'm on Wayland, on X11 it works fine (But I can't use X11 because my built-in screen is HiDPI and i need to adjust scaling for each monitor).


STEPS TO REPRODUCE
1. Take Laptop with HiDPI monitor
2. Connect external FHD monitor
3. Play a youtube video in fullscreen on that monitor

OBSERVED RESULT
1. Everything freezes for two seconds when focusing browser
2. Build-in monitor turns black

EXPECTED RESULT
No freeze and no black monitor

SOFTWARE/OS VERSIONS
KDE Neon: 6.0
KDE Plasma Version: 6.0
KDE Frameworks Version: 6.0
Qt Version: 6.6.2
Graphics Platform: Wayland

ADDITIONAL INFORMATION
It's the same with and without nvidia drivers installed (version 535).
Build-in monitor: 3840x2160@60, scaling: 175%
External monitor: 1920x1080@60, scaling: 100%
Normally I have two external monitors connected and one time the problem were gone after disconnecting the second monitor. But I didn't manage to reproduce this.
It also happened once that changing the HiDPI monitor to FHD fixed the issue.
It doesn't happen on my second laptop with build-in FHD monitor.