Login and password will not change

I tried to reproduce as well but could not. Autologin works fine with lightdm.conf set as mentioned by @mdooley.

@Rick_Rufenacht, you seem to have upgraded from 20.04 instead of a clean install. Is that so? You had issue with shutdown indicators (which btw you solved by yourself :+1:). Could it be an incomplete/improper upgrade?

Can you please provide output of following commands? Menu->System Tools->MATE Terminal. Type each of the below, one line at a time. Copy-paste the output here.

whoami
lightdm --show-config |& awk -F= '/greeter-session=/{print $2}'
cat /etc/lightdm/lightdm.conf
cat /etc/lightdm/slick-greeter.conf
cat /etc/lightdm/lightdm.conf.d/90-arctica-greeter.conf
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