The new app combines the authentication needs of Microsoft accounts for individuals plus Azure authentication (there were separate apps until now).
There’s a provision for organizations, schools etc. that require devices to be registered with them.
The Microsoft app can also give authentication codes for other accounts like Google or Facebook.
Just like the ‘old’ authentication app, it can work offline or online.
When online, you’ll see authentication requests pop-up for approval,
If offline (or the request doesn’t appear) then the Authentication app will still work. For the new app, offline codes appear on a rolling basis (not just on request, as in the old app) with a countdown to show how long the current code will last.
Offline authentication codes are time based and expire quickly so you need to enter the code on the other computer/device promptly.
Once you’ve installed the Microsoft Authenticator and linked it to your Microsoft Account, you can remove the old app.