How to set transparent background on Compose Multiplatform view on iOS?

Question

I have the simplest setup in Kotlin with org.jetbrains.compose v 1.4.0

fun MainViewController() =
    ComposeUIViewController {
       Button(onClick = { }) {
            Text("Click me")
        }
    }

On iOS i have:

struct ComposeView: UIViewControllerRepresentable {
    func makeUIViewController(context: Context) -> UIViewController {
        MainIosKt.MainViewController()
    }

    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {}
}

struct ContentView: View {
    @State var showSettings = false
    
    var body: some View {
        VStack {
            
            ZStack {
                Rectangle()
                    .fill(.red)
                    .frame(width: 500, height: 500)
                ComposeView()
                    .padding(EdgeInsets(top: 140, leading: 140, bottom: 140, trailing: 140))
                
            }
        }
    }
}

There is a white background obscuring the red rectangle even if not set specifically. I would like to have transparent background so that I can overlay compose UI over other iOS content like camera feed.

Tried to:

1. change compose theme background & surface
2. change ComposeView modalPresentationStyle to .currentContext or .overCurrentContext
3. change ComposeView vc.view.backgroundColor = UIColor.clear

But the white background is still present. Is that not supported for now or am I doing something wrong?