On iPhone X-class devices, the infrared hardware in the Face ID/TrueDepth system is not exposed as a normal camera through Apple’s approved iOS APIs. In practice, that means you can’t use it for standard infrared photography in a supported way, and third-party apps don’t get direct access to its raw IR camera feed via public SDK calls.

So for normal users and App Store apps, it is effectively limited to Apple’s intended functions such as Face ID and related depth/biometric features. While undocumented/private methods may exist, those are not part of the supported developer API and aren’t a practical or approved route for photography use.