Hi @Sebastian_Schumacher, did you enable IMAP for your user account?
This should be configurable in your Exchange console at Sign in to your account for each user:
If IMAP is enabled for your account, did you create an app password for your Microsoft 365 account? This should be possible via My Sign-Ins, though I think only if you’re not an administrator of your MS 365 account.
An alternative could be the use of the designated Outlook node instead of the generic IMAP node. I’ve quickly tested a workflow like this to fetch new emails and mark them as read:
The only downside is that you’ll need to run this workflow in intervals rather than using a purpose-built trigger. On the plus side, you won’t have to bother with IMAP authentication in MS365.
Let me know if you have any questions on this!