It started working. I find that no less disturbing. I tried it dozens of times over two days.
I did a couple of fresh installs of Duplicati on this computer (another story). I was trying to restore backups from .json files. I had it working once, had to wipe my drive and reinstall. I could not get past Oauth.
I got the icon to change color by saving a dummy configuration. It failed at least once after that so no reason to think I solved anything.
I believe there was a bug in the 126.96.36.199 beta (and a few later canaries) that caused the icon to show red after install until the first successful task action (such as a backup). Would explain your red icon experience?
As for the OAUTH issue, I believe that the authorization is done through the Duplicati OAUTH server were down (which happened a few weeks ago for a short while) everybody using OAUTH should have had issues. Since we didn’t see that (as far as I know) I think that points to an issue with your machine getting to the OAUTH server.
Granted, that’s no improvement - the end result is that you couldn’t use Duplicati for your backups. But it makes it harder to pin down the actual cause. If it happens again, do you have another machine you could test with?
Oh, this didn’t happen to start on March 16th, did it? It sounds like Google made some changes that might have tripped up Duplicati for a short while…