Comment # 10 on bug 1176195 from Fabian Vogt

(In reply to Maximilian Trummer from comment #9)
> Alright, so instead of rolling back to a previous snapshot, I just did
> ># zypper rm --clean-deps patterns-sway-sway
> and now the Plasma X11 session starts fine.
> 
> Any idea what could cause this? An additional desktop causing Plasma to fail
> sounds very strange.

I have the suspision that it puts QT_QPA_PLATFORM=wayland into /etc/profile or
similar. That would be absolutely broken.

openSUSEway does exactly that, apparently:
https://github.com/openSUSE/openSUSEway/blob/37585c7e6e0d095de8429afe4de4271c935be15b/openSUSEway.sh#L4

Did you have openSUSEway installed?

Reassinging to openSUSEway maintainer.