Licensing

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See Microsoft 365 guidance for security & compliance - Service Descriptions | Microsoft Docs:

Microsoft Defender for Identity services aren't currently capable of limiting capabilities to specific users. You must license every user you intend to benefit. In scenarios where one user may have multiple accounts in Active Directory, for example, different administrative accounts for different domains/forests, the requirement is to only have one license for this one person.

Similarly, there is no requirement to license service accounts, or any account that facilitates automation. Only human users need to be licensed.