I tried many things but dismissImmersiveSpace always trumps all. However I think I found a convoluted workaround. In Reality Composer Pro I copied all my individual scenes into one master scene. Then in my immersive view I used @State to create several empty entities. In the RealityView make I loaded the master scene, then used findEntity by name to populate the @State entities, and content.added my first scene. I then used a tap gestures to set @State bools that RealityView update can use to switch to my other scenes. It's very convoluted to get around the dismissImmersiveSpace behavior of killing off both old and new scenes described above. I will say that the performance is very good and probably better than doing multiple async scene loads. Unfortunately this workaround involves keeping a lot of state in the immersive view. I would welcome a better suggestion.

apparently some component update caused this. In the past I have always used automatic signing and I just had to select the team the first time I opened the new unity built xcode project. Apparently in the past when I did this xcode then filled in the team in all necessary build settings. Now I figured out that xcode just fills in the team for release. The fix is in build settings to select the team in the top level Development Team pull down and every underlying setting gets updated