Thomas.Poett@TEAMS (MVP Teams and Cross-Tenant Migration Specialist)

How and when to decommission your on-premises Exchange servers in a hybrid deployment | Microsoft Learn I provide you the link and a simple answer But a lot BUT: Note It's recommended that you leave the Exchange Hybrid Deployment feature enabled in cloud sync or Microsoft Entra Connect.

This is an know bug within Teams. This issue is happening on desktop and mobile version only, if you had installed the Teams app before and changed / created a new Microsoft M365 Tenant with the same user name (UPN/ SIP) Solution: Uninstall Teams App Delete all Teams references and folders Reinstall Teams App Login normally