I’ll chime in to say that it’s happening to me as well. All the outlook.com accounts cannot connect. Making a new account entry works (it authenticates with the Microsoft popup for the password) but then fails to actually connect or do anything.
I have a custom domain that also has a microsoft outlook backend and none of them log in as well. They all give the red triangle.
I can log onto all these accounts via the outlook website, and my android phone works as normal, so this is an emClient thing.
The red triangle thing happens once in a while, but clicking it usually just reconnects so I assume it’s just an internet hiccup, but this time it’s not going away. Seems to be a larger issue somewhere.