This could happen if provisioning is done without federation being enabled.
As per Apple Business Manager User Guide
Federated authentication must be turned on for the domain before you select the type of syncing and test the connection
If federation is already turned on when the Azure AD accounts are sent to Apple Business Manager, you will not see an activity, but accounts will still sync from the federated domain.
Kindly follow Configure the federated authentication process to enable federation and do let me know if you have any queries.
Thanks,
Akshay Kaushik
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