I ran into something similar on Linux Mint. Never seen my installation kill itself before until this. Ended up booting into Recovery mode from the grub menu, and rolled back using Timeshift restore.

For me, the culprit was the ubuntu-drivers-common update, because after I rolled back, I was able to install all the other updates without issue. I just blacklisted this one update to keep it from showing until the next version is released.

Try booting into console mode. Maybe there was a botched update that needs to be fixed. Below are some instructions on how to boot into tty.

https://www.linuxuprising.com/2020/01/how-to-boot-to-console-text-mode-in.html

Try switching to virtual console (alt+ctrl+F<1-6>). If it does not work, reboot with alt+sysrq+REISUB (sysrq is the same key as prtsc, REISUB must be typed sequentially).

something similar happened to me lately (on linux mint): i’ve somehow lost xorg and cinnamon due to botched wine install or maybe uninstall. what worked for me: i was able to install them again without gui, reboot (this time getting gui back) then run timeshift (that worked somehow) to restore to yesterday’s backup. note: you will be probably able to access your files in cli, and if in doubt back them up, then if all else fails you can spin up new install of your distro. it’s most likely recoverable but it will take an evening in the worst case

since then i’m making full backups every month

Something funky is probably going on in one of your updated packages. After reboot, are you able to get into the desktop?

Reminds me of that time Linus (of Linus Tech Tips) accidentally uninstalled his desktop when he’s trying to install Steam on his Linux Mint desktop. Turns out it was due to botched dependency list in the community steam package, which cause apt to prompt to uninstall gnome when he tried to install Steam, and as usual he just proceed without a second thought lol.