Comment 12 for bug 1677327

Just happened to me as well. "Just update the system" proved unexpectedly hard since the "bad" update broke X and I couldn't log in using the GUI.
Had to switch to the plain terminal and update manually from there. After that and a reboot, my system was working again.

To anyone unfamiliar with applying non-gui workarounds:

1. From the graphical login screen (that is, if you make it there), switch to the console by pressing CTRL + ALT + F1 simultaneously. If your system is broken to the point that you're dropped to a root shell, skip to step 3.
2. Log in with your username and password
3. Check for new updates: sudo apt update
4. Install updates: sudo apt dist-upgrade
5. When all updates have been installed, reboot the system: sudo reboot