Thanks all for reporting! We should have this fixed shortly.
Yes this is related to a Cross-Origin-Opener-Policy change.
Breaking auth on 3rd party apps was not intentional. Unfortunately testing 3rd party apps isn’t easy in our test environments so this issue has slipped through.
For those concerned, our auth screen makes it very clear when you are authenticating a 3rd party app (with or without that COOP). There is a prominent informative warning.
