OatPotato [they/them, she/her]

If you still need help:

1. Open a TTY (Ctrl+Alt+F3 for example, works from F1 to F6 but depending on Wayland or Xorg F1, F2 and/or F6 may be used so F3 should be good, otherwise try another one).
2. The TTY will ask for your username and password, so login with your normal user (not root).
3. You shoud get to an interactive shell, so you can go to the Gnome extensions directory (cd ~/.local/share/gnome-shell/extensions/).
4. You can now remove the problematic extension (rm -r …).
5. Now either you reboot your computer (the reboot command will be enough to restart the computer), this will ensure you don’t keep a remaining session and you’ll boot in your login manager (GDM I guess).

Hope it helps!

You can run pacman -Qe to list explicitly installed packages, beware of packages you may have installed manually as optional dependencies of other packages.