I've just upgraded from Mate 18.04 to Mate 20.04. After the upgrade finished and rebooted, the "symbol 'grub_file_filters' not found" error was displayed. It seems that my previous boot disk is no longer bootable. Instead my SSD disk is now the boot disk, but GRUB still points to the previous boot disk.
That's my assumption but, not being a techie, I'm wary of making changes that I don't understand and cannot undo.
Has anyone else encountered this problem? How did you fix it?