Your data will be there, but you will have to recreate all shares, users, tasks, calendars settings , everything.
because all that is on the database, which seems to have the problem.
I'd say, use your backup, at 20.0.9, file the issue on nextcloud's github (with the template filled).
They might point you to an easy solution, Otherwise, wait until 21.0.1 is out (it's scheduled for 20-may-21) .
If it fails then, and no solutions on github, they you can go ahead and re install.