Hello all,
running in some problems with the configuration of osTicket and M365. As described below I use Exchange Online. Focusing on IMAP I try to fetch Email. I tried different approaches for the Test:

1:
I disabled all security related settings on the M365 Tenant like Security defaults and MFA and enabled Basic Auth for IMAP and SMTP as described here Enable Basic authentication in Exchange Online | Microsoft Docs and configured the client settings as described in POP3 and IMAP4 in Exchange Online | Microsoft Docs. Also enabled Trusted IPs in MFA to lower security. Ending up with Can not authenticate to IMAP server: AUTHENTICATE failed. Reversed all security related settings.

2:
Configured App Password as described here Configure app passwords for Azure AD Multi-Factor Authentication - Azure Active Directory | Microsoft Docs, made the necessary changes on osTicket «Password». Ending up with Can not authenticate to IMAP server: AUTHENTICATE failed.

osTicket Version v1.16.1 (b42ddc7) — Up to date
Web Server Software LiteSpeed
MySQL Version 5.7.26
PHP Version 7.4.27

Runs in a shared environment at my Hosting Provider, dedicated Plesk access.

Azure Active Directory security defaults | Microsoft Docs

Configure app passwords for Azure AD Multi-Factor Authentication - Azure Active Directory | Microsoft Docs

Configure Azure AD Multi-Factor Authentication - Azure Active Directory | Microsoft Docs

Configure app passwords for Azure AD Multi-Factor Authentication - Azure Active Directory | Microsoft Docs

Thank you for any hint or help.