Upgrade problem to 2.1 from 2.0.6.3_beta probably fits, except 2.2 is now the latest Stable.
That’s pretty much it. 2.0.8.1 did upgrades to 2.1 OK, but no point installing 2.0.8.1 manually.
Upgrade 2.0.7.1_beta_2023-05-25 to 2.1.0.2 gives the very long version of the updater story.
Download Duplicati Today will offer the latest Duplicati which you would then manually install.