Info.plist

<dict>
  <key>UIApplicationSupportsMultipleScenes</key>
  <true/>
  <key>UISceneConfigurations</key>
  <dict>
    <key>UIWindowSceneSessionRoleApplication</key>
    <array>
      <dict>
        <key>UILaunchStoryboardName</key>
        <string>LaunchScreen</string>
        <key>UISceneConfigurationName</key>
        <string>Default Configuration</string>
        <key>UISceneDelegateClassName</key>
        <string>$(PRODUCT_MODULE_NAME).SceneDelegate</string>
      </dict>
    </array>
  </dict>
</dict>

NewAppDelegate.swift

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
    // Moved window creation to the SceneDelegate below
    return true
  }

  // Added this method:
  // Here we tell iOS what scene configuration to use
  func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
    connectingSceneSession.userInfo?["activity"] = options.userActivities.first?.activityType

    // Based on the name of the configuration iOS will initialize the correct SceneDelegate
    return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
  }
}

OldAppDelegate.swift

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
  var window: UIWindow?

  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
    // ...
    
    window = UIWindow(bounds: UIScreen.main.bounds)
    window.rootViewController = PostNLRootViewController()
    window.makeKeyAndVisible()

    // ...

    return true
  }
}

SceneDelegate.swift

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
  var window: UIWindow?

  func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let windowScene = (scene as? UIWindowScene) else { return }
   
    window = UIWindow(windowScene: windowScene)
    window.rootViewController = PostNLRootViewController()
    window.makeKeyAndVisible()
  }
}