Problem
When you try to log in into GNOME, you’re immediately returned back to the login screen.
Note: This issue can have many different causes. This documents one of them related to accessibility settings.
Cause
There’s a bug in GNOME that makes it crash, when the Mouse Keys accessibility feature is turned on in GNOME Settings (which allows you to control your mouse using the numeric block on your keyboard).
Related Issues
GNOME bug: Crash when starting Wayland session with mouse keys enabled (#3708) · Issues · GNOME / mutter · GitLab
Solution
You need to disable the mouse keys feature to avoid this issue.
Option 1)
If you still have an X11 session installed (it’s no longer available by default on new installations, but can be present on upgraded systems), you can select it in the cog menu on the login screen (before inputting password, select GNOME on Xorg). After logging in, go to GNOME Settings → Accessibility → Pointing and Clicking and disable Mouse Keys. Then log out, select the default GNOME session (based on Wayland, more secure), and log in again.
Option 2)
You can disable mouse keys from the text mode. Press Ctrl+Alt+F3 to switch to a text terminal. Log in, and run this command:
gsettings reset org.gnome.desktop.a11y.keyboard mousekeys-enable
Type exit to log out, press Ctrl+Alt+F1 to switch to a graphical login manager, and log in. It should work now.