Using Outlook for Android in business environments for email and scheduling
I had the same symptom, but it looks like it might have multiple causes.
It started with one of my organisation's workers not being able to check emails in Outlook mobile on Android (Samsung Galaxy A20). It asked her to 'sign in' but each time she did it just glitched (no error, just stopped trying and then asked to sign in again). Restarted phone.
I tried resetting the account, removing the account, clearing cache & data in Outlook.
Outlook up-to-date with the latest
Outlook is required by our InTune policy so I didn't try uninstalling it.
It turns out she couldn't sign in to ANY Microsoft 365 app - OneDrive, Word, Excel, PowerPoint, Office Lens, getting a similar error each time. I tried various suggestions from here but none worked.
The solution that worked for me (I think this only applies to devices managed through InTune):
In the phone's Settings app under 'Accounts', there was a 'Work account'. I removed that acccount, then was able to sign into all the Microsoft 365 accounts again, and the 'Work account' appeared back by itself too after re-signing in.