Related (duplicate?) issue regarding immersive-ar mode here: https://developer.apple.com/forums/thread/826845

Related request for immersive-ar mode request: https://developer.apple.com/forums/thread/826845

Related question, regarding immersive-ar mode for WebXR: https://developer.apple.com/forums/thread/826845

A long time ago, but I'm seeing the same issue with Unity 2022.3.2f1 - did you ever get this working?