My idea of a workaround. download the Tritone sound files. incorporate into your application. Specify the name of the tritone sound source in UNNotificationSoundName. But, this workaround may have copyright problems.

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   }

I was able to resize using HTML. Thank you.