Error when connecting to Exchange account

I am facing issues adding my exchange account.

The error message says: “Der Server wurde gefunden, aber die Authentifizierung ist fehlgeschlagen. Überprüfen Sie Email-Adresse und das Kennwort”. However, both email / user name and pwd are correct

We are talking about a Microsoft 365 Business Standard cloud service.

I am using:
MacOS Big Sur 11.2.3 on M1 chip, eM Client v. 8.1.1083

I have an eM Client 8.2.1237 installed on Win10 and here everything works fine.