The alt.updates.duplicati.com resolution error part is known because the name is not set up, however elsewhere in that article there seem to be some mysterious failures in updates quite recently. It’s conceivable that the system is under repair, or partially disabled to cut updates off at this point instead of a later failure…
The alt version of updates is only used when the main one is down. Right now, the main one is giving 502s.
Duplicati.AutoUpdater.exe check is a way to keep an eye on things, as shown in this debug sequence.