Resolved ARFoundation 4.x: No more XRFaceSubsystemDescriptor on iPhone Xs

The Documentation for

Code (CSharp):

1. SubsystemManager.GetSubsystemDescriptors

is limited:
https://docs.unity3d.com/ScriptReference/SubsystemManager.GetSubsystemDescriptors.html

However these posts
https://forum.unity.com/threads/how-to-detect-if-face-tracking-is-available-on-a-device.923939/
https://forum.unity.com/threads/arfoundation-face-tracking-step-by-step.600313/
suggest, that the method could be used to test, if Face Tracking is available on a device.

We expected a list with (at least) one

Code (CSharp):

1. XRFaceSubsystemDescriptor

to be returned so far.

On an earlier version of ARFoundation (2.1.8) this worked for all iOS Devices with TrueDepth Camera.
After an update to Unity 2020.3 and ARFoundation 4.1.1 (also tried other 4.x versions), the list returned is empty (tested on an iPhone Xs).

What could be the problem here?

 

Changing

• Project Settings → XR Plugin-management → ARKit → FaceTracking (on)
• Project Settings → XR Plugin-management / iOS PLugin Providers → ARKit (on)

fixxed the problem.