I haven't used timeshift in at least three years so Im going to give you this instead of relying on my possibly faulty memory.
https://itsfoss.com/backup-restore-linux-timeshift/
Command line instructions
https://dev.to/rahedmir/how-to-use-timeshift-from-command-line-in-linux-1l9b
Hay if the restore works might hold off on doing an update for a few days just too see if kubuntu had pushed a bad update. If they did they did they should fix it pretty quickly when they get a bunch of people with broken systems.