Xcode 11 backward compatibility: "UIWindowScene is only available in iOS 13 or newer"

The template in Xcode 11 uses a scene delegate. Scene delegates and the related classes are new in iOS 13; they don't exist in iOS 12 and before, and the launch process is different.

To make a project generated from an Xcode 11 app template backward compatible, you need to mark the entire SceneDelegate class, and any methods in the AppDelegate class that refer to UISceneSession, as @available(iOS 13.0, *).

You also need to declare a window property in the AppDelegate class (if you don't do that, the app will run and launch but the screen will be black):

var window : UIWindow?

The result is that when this app runs in iOS 13, the scene delegate has the window, but when it runs in iOS 12 or before, the app delegate has the window — and your other code may then need to take account of that in order to be backward compatible.

Could you please add this line code like the following

STEP1:-

@available out the SceneDelegate.swift

@available(iOS 13.0, *)
class SceneDelegate: UIResponder, UIWindowSceneDelegate {

//...

}

STEP2:-

@available out some methods in AppDelegate.swift

// AppDelegate.swift

@available(iOS 13.0, *)
func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
    // Called when a new scene session is being created.
    // Use this method to select a configuration to create the new scene with.
    return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
}

@available(iOS 13.0, *)
func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
    // Called when the user discards a scene session.
    // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
    // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
}

STEP3:-

You should declare window property in AppDelegate.swift file like var window: UIWindow?

class AppDelegate: UIResponder, UIApplicationDelegate {

     var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }