Scene Commands, how to create a submenus???

You can create submenus using the Menu type (née MenuButton). This also works in other menu types, like context menus and pop-up buttons.

Code Block 
@main
struct TestApp: App {
    var body: some Scene {
        WindowGroup {
            Text("Hello, SwiftUI!").padding()
        }
        .commands {
            CommandMenu("Example") {
                Button("Menu Item", action: ...)
                Divider()
                Menu("Submenu") {
                    Button("Menu Item", action: ...)
                }
            }
        }
    }
}

FYI, there are some known issues that prevent state changes from updating menu bar menus as expected, which more or less prevents sharing state between your main menu and your windows. This will be addressed in a future seed.