20.3 to 21.0 failed upgrade/wont restore to Timeshift

I used the mint proper procedure and it showed that the upgrade was successful. However at startup the list of things wrong was long but I was able to use 21.0 and do updates thru update manager for a few days. Then a few days later I got "root file system has 0 bytes available". I thought all the versions of kernals was the issue but thought it would work itself out. It didn't. I had created a snapshot with timeshift during yjr upgrade so I tried to go back to that. It didn't take. I can bring up the grub menu and it gives me 2 choices for 20.3, normal and advanced. Advanced gives me options for several kernels and option for recovery mode. I tried about all options and they all run a few pages of code and end with a kill kernel panic message. This is where I'm stuck. I'd simply like to restore 20.3 which appears to be there but somehow got jacked up by the successful 21.0 upgrade. The upgrade went to 22.04 from 20.04 and 20.3 support ends in 9 months. How a reported successful upgrade went bad I don't know? Thanks