You actually only need to enable Scene Semantics (available for iOS at extensions 1.40+).

1. update the arcore extensions to 1.40+ so you have the scene-semantics (semantic segmentation) also working for IOS.

• Download newest tgz from arcore-unity-extensions, 1.41 atm at https://github.com/google-ar/arcore-unity-extensions/archive/refs/tags/1.41.0.tar.gz
• in Packages/manifest.json replace the 1.37 to 1.41 wherever you put it, eg "com.google.ar.core.arfoundation.extensions": "file:../Assets/Packages/arcore-unity-extensions-1.41.0.tgz",

2. switch build to iOS and set up the project as usual (see here): set camera and location usage description in Project Settings > Player, enable Apple ARKit in XR Plugin management, and add your iOS API key to the ARCore extensions settings, as well as enable Semantics on iOS there.

3. Then finally to also enable location permissions, which work differently on iOS (You'd get a Failed to configure the session with error: ErrorLocationPermissionNotGranted error otherwise)

Just create a new game object in the scene, call it "LocationMonitor" or whatever, and create a new script with a similar name (LocationMonitor.cs) to it with the following code:

public void OnEnable()
{
    Input.location.Start();
}

public void OnDisable()
{
    Input.location.Stop();
}

Turns out thats all thats really needed to make it work for iOS.

See it working on my iphone: https://twitter.com/graphific/status/1748744479832449074