You mention timeshift, did you restore to the working snapshot after selecting it in grub, then reboot AGAIN?
Booting a snapshot, does not restore from it. When booting a snapshot from grub, you need to open timeshift, restore the snapshot, then boot up a second time (this time without selecting it in grub).
Otherwise, you didn’t really restore it, you just booted into it, and if you re-attempted the broken update, messed the snapshot up, too (leaving you with no working snapshot to go back to).
You mention timeshift, did you restore to the working snapshot after selecting it in grub, then reboot AGAIN?
Booting a snapshot, does not restore from it. When booting a snapshot from grub, you need to open timeshift, restore the snapshot, then boot up a second time (this time without selecting it in grub).
Otherwise, you didn’t really restore it, you just booted into it, and if you re-attempted the broken update, messed the snapshot up, too (leaving you with no working snapshot to go back to).