After I started up my computer, having updated the last time I used it, going past the log in screen just shows the lock-screen background for a little bit, before a black screen with just a cursor. The Lock Screen still works if I shut the laptop lid or leave the computer enough, but the screen doesn’t seem to turn off properly when shutting the lid and most keyboard shortcuts don’t work, though I can still go to tty.
I tried updating. I tried reinstalling Cinnamon. That didn’t work, but installing lxde and selecting that at login worked, but Cinnamon still doesn’t.
I eventually found out that right clicking the black screen Cinnamon desktop still works, and I can get windows such as the terminal like that, but the windows won’t move or resize.
Probably just going to do a new install.
Go to a TTY by pressing Ctrl + Alt + F3. Replace F3 with F4, F5, F6 etc if you are already on that TTY. Once you are in TTY, login with your user and its password. Then run cinnamon --replace. If it runs without any problems, the problem might be related to your display manager. If it doesn’t start, you should see the errors.
This seems to be an error that traced back to Mutter, since Muffin (CInnamon’s window manager) is a fork of it I believe they are related. Maybe an upgrade solve this? The post says you are on 21.3, so while on TTY, do an upgrade to see if that works.
sudo apt dist-upgrade