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You can use PowerShell to turn off directory synchronization and convert your synchronized users to cloud-only
To turn off Directory synchronization:
First, install the required software and connect to your Microsoft 365 subscription. For instructions, see Connect with the Microsoft Azure Active Directory Module for Windows PowerShell.
Use Set-MsolDirSyncEnabled to disable directory synchronization:
PowerShellCopy
Set-MsolDirSyncEnabled -EnableDirSync $false
Note: If you use this command, you must wait 72 hours before you can turn directory synchronization back on.
After the user become "Cloud-Only" you can remove your on-premises AD DS
Hope this helps!
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