Yesterday I upgraded my Ubuntu 20.04 Pixelbook (full Ubuntu, no Chrome nonsense) to 22.04. However, the system now gets stuck immediately after login. After I successfully log in, the login prompt disappears but the wallpaper & cursor remain -- however, nothing further changes even after I wait a long time. The cursor is still responsive, but no combination of clicks or keypresses seem to do anything. Note that a single press of the Power button at this stage does seem to successfully shut down the computer.
Even worse, I don't seem to be able to bring up the GRUB loader upon reboot: holding down either or both SHIFT keys doesn't seem to accomplish anything, and I'm brought right back to the login screen.
Suggestions would be most welcome!
EDIT: Holding down 'ESC' during startup also doesn't bring up the GRUB options. Quickly & repeatedly pressing 'ESC' during boot does cause a change: the screen goes black and the login screen never appears. But no constructive changes.
EDIT2: Typing CTRL+ALT+F2 (or F3, etc) at the login screen just brings me to a blank screen, where I'm again stuck. But the system is still slightly responsive, in that pressing the power button causes the machine to shut down after a few moments.
EDIT3: Logging in as a different user or as root has the same effect.
EDIT4: typing sudo systemctl start gdm' successfully brings up the old GDM, which lets me log in -- the full Ubuntu desktop shows up, as normal. But if I replace gdm' with `lightdm' then it's the same as my initial problem described above.
