KDE Plasma 6 doesn't start, a black screen shows up instead

Ever since I updated to Fedora KDE 40, when I log into my main user KDE Plasma doesn’t start. What does happen varies based on changes I make - right now it goes into a longer than usual KDE splash screen before I get a black screen with a cursor (and Discord which opens automatically). Most importantly, KDE Plasma works perfectly on a new user.

I know there’s a similar issue on Nvidia cards… but I use Radeon.

I was told my computer thinks another compositor is running, and that it’s something in the user configuration. I was given multiple suggestions as to where the problem could be - KDE config, systemd config, environment variables, PAM stuff. But I’m still not sure where to start.

I have an asciinema recording of what happens when I try to start KDE Plasma on Wayland, but I can’t post links :frowning:. You can just search my username on there. When I try to run it on X11, I’m often told that /home/mikwee/.serverauth.6641 does not exist.

I’m really tired by this point, and I hope you can help me. How can I troubleshoot this problem? Thank you.