This might be common knowledge, but I just found it out this morning, so wanted to pass it along. Although there is no longer a Microsoft Authenticator app for the Apple watch, you can still use the watch to approve/ deny logins. This only works when there is an Approve/ Deny pop-up, not if you have to type in numbers. But it does work.
You need to make sure that the setting 'App Lock' is turned off in the iPhone app's setting, but then instead of just getting a notification your watch that there is an Authenticator request, you actually get the ability to approve or deny right from the watch.
You need to make sure that the setting 'App Lock' is turned off in the iPhone app's setting, but then instead of just getting a notification your watch that there is an Authenticator request, you actually get the ability to approve or deny right from the watch.