Can't upgrade to Ubuntu 21.04 : "Restoring original system state. Aborting"
Solution 1:
Removing snapd with sudo apt-get purge snapd was the solution.
Solution 2:
Was also affected by this. After removing snapd it still affected me. The last comment on this thread pointed the fix that worked for me https://github.com/microsoft/WSL/discussions/3489#discussioncomment-961901
I had to remove both snapd and screen!
1 - sudo apt-get purge snapd
2 - sudo apt-get purge screen
And then the upgrade ran smoothly. If it is still failing, you can cat /var/log/dist-upgrade/main.log to see what's causing you to fail!