Comment by dagmx

It’s specifically using the ARKit facial tracking that gives you FACS blend shape values

https://developer.apple.com/documentation/ARKit/tracking-and...

This plugin to blender is basically just receiving those values from the OS API and applying it. It’s a fairly common integration and almost all alternatives depend on ARKit on an iPhone as a result rather than implementing any algorithms themselves.

Variations of this plugins functionality have existed since the introduction of the iPhone X in 2017.