How do I check whether Stage Manager is enabled?

If you just want to check if Stage Manager is enabled this code might help.

But, this process is not perfect.

can not switch on/off.

// AppDelegate version
    var isStageManager: Bool {
        guard UIDevice.current.userInterfaceIdiom == .pad,
           let appDelegate = UIApplication.shared.delegate as? AppDelegate,
           let screenHeight = appDelegate.window?.windowScene?.screen.bounds.height,
           let windowHeight = appDelegate.window?.bounds.height else { return false }
        return screenHeight > windowHeight
    }

// SceneDelegate version
   var isStageManager: Bool {
    guard UIDevice.current.userInterfaceIdiom == .pad,
       let sceneDelegate = UIApplication.shared.connectedScenes.first?.delegate as? SceneDelegate,
       let screenHeight = sceneDelegate.window?.windowScene?.screen.bounds.height,
       let windowHeight = sceneDelegate.window?.bounds.height else { return false }
    return screenHeight > windowHeight
  }