Turns out I could crash ksplashqml quite reliably rendering my kde setup unusable simply by having a bad XDG_DATA_DIRS configured in my .zshenv file.

I’m not sure what caused it. But it might be because it was already set, or that it ended with a :

img.png

Edit

Actually a bit more looking around and it turns out it is if XDG_DATA_DIRS contains the same entry twice it crashes.