Unfortunately UIHostingController allows you to integrate SwiftUI views only in existing UIWindow. You won’t get immersive Full Space this way.

I've stopped with the same problem - I can't implement billboards by looking at AnchorEntity(.head) world position, it's always [0,0,0]

I've recently discovered that if your entity includes only flat plane meshes it won't be hovered. So make sure you have added a volume-mesh in to your entity hierarchy