Probleme mit Lightdm

[Wollie]

… oder evtl. mal schauen, ob das hier weiterhilft:

Kernel 5.10.2-2 breaks lightdm

you may want to check the logs in /var/log/lightdm. If you are using AMDGPU as driver, there is a known bug, and you have to add a setting to your grub config, to be able to boot on that kernel series. Does your PC boot on 5.9 or older kernel series? See also here for troubleshooting: