I am having the same issue. I receive a
Authentication error: SDDM:Auth::ERROR_INTERNAL "Process crashed"
Auth: sddm-helper (--socket /tmp/sddm-auth-813a821f-ede7-4ec7-baec-1d717b196737 --id 1 --start Hyprland --user xxxxxxxx) crashed (exit code 1)
Authentication error: SDDM:Auth::ERROR_INTERNAL "Process crashed"
Auth: sddm-helper exited with 1
Seems like it is a known issue and it is very annoying as I cannot log out and must reboot instead otherwise I get a black screen with a blinking cursor and no sddm/login screen.
There is a similar thread here with some suggestions: Black screen with a blinking underscore on top left