Thanks for the question, it actually made me look for the api. Looks like I misremembered it, and there aren’t actually any exposed APIs for developers regarding attention. Internally it’s used by iOS for checking when you’re looking at the screen for faceID and keeping the screen lit when you’re reading.
There are APIs for developers that expose the position of the users head, but apparently it excludes eye information. Looks like it’s also pretty resource intensive, and mainly for AR applications.
The faceID / touchID api essentially only returns “authenticated”, “authenticating”, and “unautheticated”. The prompts / UI are stock iOS and cannot be altered, save showing a reason.
This was always a known risk of having alternative app stores. Think of it from the dev’s point of view, he’s also one of the founders of AltStore. Of course an exclusive app is one of the best ways to get people onboard. Just wait for the Epic, Meta, Amazon… stores next. At least AltStore has an open-source ethos behind it.