Microsoft have made a further update to their incident reference - regarding setting up Microsoft 365 email accounts on the iOS Mail app ( EX1021490 )
"Users may be able to click "continue" when prompted and navigate back to re-entering their password to attempt to resolve impact.
If users aren't prompted but are still experiencing impact, please follow the steps in the following link:
Our recommended methods for retrieving emails on a mobile device remains the Outlook mobile app (from Apple / Google app stores) - or Outlook web via https://outlook.office.com
Microsoft have logged an issue in their system health portal - reporting that 'some users may experience issues with accessing email messages on the iOS Mail app'
Microsoft reference: EX1021490
Our recommended methods for accessing email on mobile devices continues to be the Outlook mobile app (iOS and Android), and the Outlook web app ( https://outlook.office.com )