MATE accepts my password for my username, but goes into an infinite loop after I log in and puts me back to log in screen on lightdm.
If I log in using root and use "systemctl stop lightdm" and systemctl disable lightdm", I can log in to Debian Bullseye because there is no graphic interface running.
I don't remember specifically if I could log in, with the text log in, then try "startx" but I'm sure I did, but I'm making a note to try this again, because I am going to run "journalctl -f" in another console when attempting to log in.
I do remember changing the password to the "real" user password, it made no difference, next boot, the situation was still the same.
More later.
DR