Microsoft has released a new version of the Microsoft Authenticator beta for iOS via the Apple TestFlight program. This beta version will bring the build number for the app to 5.9.4 and includes bug fixes and changes to phone sign-in. The instructions for beta testers are cryptic at best and it is not known exactly what they want beta testers to test with this build. If you want to try out the new features in this beta before it becomes available to everyone, you can sign up to beta test the app now.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-authenticator-beta-594-for-ios-released-on-testflight/