macOS complaining about SceneStorage

Using Xcode 12 beta 2 on Big Sur beta. Having a view like this:

Code Block swift
import SwiftUI
struct ContentView: View {
    @SceneStorage("selectedItem") var selection: String?
    var body: some View {
        NavigationView {
            List(selection: $selection) {
… list contents
            }.listStyle(SidebarListStyle())
        }
    }
}


When I try to compile and build this on macOS, I get this fatal error:

Code Block
Fatal error: @SceneStorage is only for use with SwiftUI App Lifecycle.: file SwiftUI, line 0


I am definitely using the SwiftUI App Lifecycle because this is a fresh new project created with Multiplatform app template.

Why do I get this error? Can I fix it somehow?
@SceneStorage isn't supported on the Mac.

And I know what you are going to ask next. No. I don't know when it will be supported, if ever.
What makes you say that it is not supported? According to API documentation, and the SwiftUI header, it also exists on Mac.

Code Block swift
@available(iOS 14.0, OSX 10.16, tvOS 14.0, watchOS 7.0, *)
@propertyWrapper public struct SceneStorage<Value> : DynamicProperty {

macOS complaining about SceneStorage
 
 
Q