I think calling it DRM is incorrect. I think Apple and its audience belief you should be able to tell if a replacement part could be counterfeit, and possibly have a security vulnerability as a result. However, it should be a one-time notice that a user can dismiss and continue using the phone’s complete functionality.

For example, if someone replaces a camera module, Face ID could technically be compromised. That said, the security for Face ID is on the device itself, and replacing the module with a third-party one, as long as they was made aware it may not be as secure as the original part, let them do what they want with their own device.

EDIT: If it were me, I would want to know a part in my phone is not directly from Apple, but I would still want the ability to determine if I want to continue using the phone like that or straight up replace it. It should be the user’s decision.