If that’s exactly what you tried to attach, didn’t it pop up an error? Regardless, try a .zip file version.
In this case (but not always) the database for the backup job as described in Database management.
Release: 2.0.6.1 (beta) 2021-05-03 talks about it a bit, mentioning 11 and 10, and giving a downgrade procedure for intentional downgrade if desired. Yours was probably accidental changes to the 2.0.6.3 update which you can find and then right-click → Properties to see if it contains 701 Files, 90 Folders.
Try looking for the 2.0.6.3 folder in C:\ProgramData\Duplicati\updates and
C:\Users\<Duplicati user account>\AppData\Local\Duplicati\updates
Please mention any other updates that you see, and also About → System info → BaseVersionName which is what runs initially, then runs the latest intact update. Here, the latest 2.0.6.3 may be damaged which might leave you on an older version such as 2.0.5.1 which doesn’t know the 2.0.6.x DB formats.
Duplicati forgets update was a case where some extra folders and files got made, but it’s unclear how.