Register Mac to Azure AD without enrolling in Intune

Solution 1:

You can't have macOS registered and compliant.

Only managed devices can be compliant.

This is by design, because Intune MDM client (Windows) or Company Portal app (macOS) has to validate device for compliance policies before marking device as compliant. And it can't do that for an unmanaged device.

This is stated in Microsoft documentation

This option requires a device to be registered with Azure AD, and also to be marked as compliant by:

• Intune
• A third-party mobile device management (MDM) system that manages Windows 10 devices via Azure AD integration. Third-party MDM systems for device OS types other than Windows 10 are not supported.

This also (probably) explains a reason you have registered Windows device marked as compliance