Thank you so much for posting here.
So sorry that we are not professional with Linux SAMBA Active Directory.
Similar discussion is here.
We could add it as member server or configured it as domain controller.
"If configured as a Domain Controller, Windows Server 2019 Essentials must be the only Domain Controller, must run all Flexible Single Master Operations (FSMO) roles, and cannot have two-way trusts with other Active Directory domains."
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