No autofill with MS Authenticator Password Manager
Microsoft has introduced its own Password Manager in the Authenticator app.
I've given it a try, first with DuckDuckGo browser: it works.
Next attempt with Vivaldi Mobile Snapshot: it does not work.
Still hoping for Vivaldi to (finally) provide proper support for the Android Autofill API.
The latest mobile snapshot includes support for the Android Autofill API and works with Authenticator.