arfoundation-samples | Example content for Unity projects | Augmented Reality library

I just started learning AR development with unity using this YouTube tutorial (https://www.youtube.com/watch?v=lelX8GGh_S8). At some point in the tutorial, the creator added a script called "Place on Plane" to the AR Session Origin. He didn't write the script in the tutorial and it seems more like a Unity script but for some reason, I wasn't able to find it in my Unity and now I'm stuck. Please, any assistance would be greatly appreciated.

Script: https://github.com/Unity-Technologies/arfoundation-samples/blob/main/Assets/Scripts/PlaceOnPlane.cs

I am running this ARKit example project https://developer.apple.com/documentation/arkit/creating_a_collaborative_session. Everything works perfectly, except that the ARParticipantAnchor's transform is always NaN (all 16 numbers in the transform matrix are NaN). Other ARAnchors all have a valid transform value but ARParticipantAnchor doesn't.

From my understanding of ARKit, after a peer iPhone joined the collaboration session, an ARParticipantAnchor is added through the delegate function session:didAddAnchors: to represent the location and orientation of that peer. After that, ARKit keeps updating that ARParticipantAnchor's transform through the delegate function session:didUpdateAnchors: to minor the real-time location and orientation of that peer's iPhone.

I have run this sample project several months ago and it went perfectly. So I am pretty confident that I am not missing any detail. But from yesterday, I could not make it work. An ARParticipantAnchor was successfully added after a peer had joined the collaboration session, and the delegate function session:didUpdateAnchors: was called every frame, but the ARParticipantAnchor's transform in session:didUpdateAnchors: was always NaN!

I also tried the Unity ARFoundation samples in this repo https://github.com/Unity-Technologies/arfoundation-samples/tree/main/Assets/Scenes/ARKit/ARCollaborationData, and it doesn't work either! I have used this repo several months ago and I am pretty sure it worked.

So, if both native ARKit and Unity have this problem, I suspect that probably there is a bug in ARParticipantAnchor after a recent ARKit update? After all, if ARParticipantAnchor's transform is always NaN, what is the point to update it every frame and share that data through the network? Could anyone tell me how to make it work? Thanks!

I am tracking images with my AR-App and whenever an image got detected there should be a plane overlaying the tracked image.
The plane should have the same dimensions and rotation as the image.
I've already tried using this code snippet but retrieving the image's children's transform yields an error because the image doesn't have any children. Following this video wasn't successful either.

Anyone got an idea on how to get the ARTrackedImage's plane information?