Duplicati has separate versions for base (such as install from .msi) and updates. If you installed 126.96.36.199 from .msi (unknown) then a check for updates would look for a newer experimental, and there isn’t one.
See Releases in GitHub or Releases in forum for that and for 188.8.131.52 to 184.108.40.206 changes (not very much because Experimental was a prerelease of Beta that time, so change was mostly very limited/specific).
The GUI could probably be improved. While I wouldn’t call lack of updates an error, this tool does better:
C:\Program Files\Duplicati 2>Duplicati.Library.AutoUpdater.exe check
No updates found
C:\Program Files\Duplicati 2>
Channels explains the concept generally.
Duplicati on Windows - two version numbers goes into lots of technical detail if you care for such things.
Settings in Duplicati shows how to find and set your Update Channel (default maybe now Experimental).
Getting information about your setup and Updating Duplicati may help. Note how they speak of channels.
Any details on that? I’ve seen .msi install sometimes wind up with missing files unless I uninstall old first. Uninstall won’t mess with your data, but install of 220.127.116.11 beta might change your default channel to beta.