I fixed it.
To try something else, I decided to add another user, to test if it’s a user problem. With that new user, I could login just fine. With some trial and error I figured out the problem was something in the .config directory (not sure what exactly). With the maybe not very elegant solution mv .config config, I could login again.
I might try to figure out what file specifically was causing the problem tomorrow.
Thanks for the help, it was a nice first forum experience!