Thanks to the great backup program “Timeshift”, errors even fatal ones can be corrected.
But I have seen extensions run havoc with the desktop, because they are not examined enough before allowed to be published and downloaded.
If you still have Ubuntu 20.10 installed then please open a new bug by running:
ubuntu-bug gnome-shell
Please report bugs only using the ubuntu-bug command, or via launchpad.net in future. Not here.