Hi @Damian M
Cutover Migrations are not allowed if dirsync has been enabled for the tenant.
While you can re-enable dirsync once the cutover migration is done.
There have been several threads discussing this topic, which may be helpful.
For your reference:
Disable DirSync - Perform cutover migration - Re-enable DirSync
Exchange cutover migration will work with AAD connect sync user?
Using Dir Sync after Cut over migration
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