Using Outlook for Android in business environments for email and scheduling
Hi, I had the same problem on my device and fixed it. I thought I'd share.
If the account is a work or school account which requires you to use the authenticator app, try closing out of Outlook and opening Authenticator. Go to settings within the authenticator app and turn battery optimization off. Leave the app running in the background, open up Outlook again, and attempt to sign in.