Please check that Wayland has NOT been disabled in /etc/gdm3/custom.conf
And if the login screen issue happens again then from Ctrl+Alt+F4 please run:
journalctl -b0 > failednow.txt
and attach the resulting text file here.
BTW, the very fact that you can see an X cross on a black screen means you're using X. Please disable auto-login and try selecting 'Ubuntu on Wayland' on the login screen.
Please check that Wayland has NOT been disabled in /etc/gdm3/ custom. conf
And if the login screen issue happens again then from Ctrl+Alt+F4 please run:
journalctl -b0 > failednow.txt
and attach the resulting text file here.
BTW, the very fact that you can see an X cross on a black screen means you're using X. Please disable auto-login and try selecting 'Ubuntu on Wayland' on the login screen.