https://gist.github.com/simplebunsen/f893aa6406a23c96b04ae557b6fb6191
crashing before it gets to the main menu.

This issue has been marked as stale because it has been inactive for 3 weeks. It will be closed if it remains inactive for another 3 weeks.

This issue has been closed since it has been inactive for 3 weeks since it was marked as stale.

I can see the following line in the stacktrace

at de.keksuccino.fancymenu.menu.fancy.loadingdarkmode.DarkResourceLoadingScreen.func_230430_a_(DarkResourceLoadingScreen.java:120) ~[fancymenu:1.0] {re:classloading}

Out of curiousity, could you try loading without fancymenu enabled and see whether it's still an issue? Could be a mod compat issue in that case

Trying that. It's very weird, because I've loaded both mods in parrallel very often and suddenly, without changing anything, it crashed like that.
Actually, trying in that exact same configuration which had the crash earlier, I can start the game without problem again now... I really don't know anymore...