pacman -Rscn gnome gnome-extra
Arch Linux
Many thx. Will try that as a second user, just in case that the current user block something.
My main issue is, that I can't shutdown or reboot from within the quick settings panel anymore. If I do that, applications do close, but the computer doesn't shutdown. However it's working fine from a terminal.
Programs that run as regular users usually store their config in ~/.config/ or ~/.local/share/ so look in those places for config files relating to gnome. There might be a lot. It may be easier to backup then remove the both directories, saving only the config of your most important programs. Some config is stored in dconf, which should also be in here.
Worked fine so far. I have just renamed .config and .local directory's for later use and reinstalled Gnome. So far this seems to work. In my tests today, I could shutdown/reboot succesfully with every try. Hopefully this is a permanent fix. Since I have all the old files, maybe I find the time to check them for errors. But I fear I didn't have so much time. Anyway, many thx for your tips which helped to fix the issue for me.