For those with existing projects that rely on a SceneDelegate and are primarily UIKit-based, I am curious how one might launch a window with a style of volumetric or an ImmersiveSpace. Is this possible without having a SwiftUI-based @Main entry point?
I've stuck with the same problem.
ImmersiveSpaces are not possible per Apple reply here: Link
Indeed, ImmersiveSpace is a SwiftUI-only API – in order to use it, you need to use SwiftUI's app lifecycle.
Note that parts of your apps can still be using UIKit though, using UIViewRepresentable and UIViewControllerRepresentable.