Since the chapter was written, I think there has been an update to the code generated by XCode for new projects. Therefore, example of manually adding a second tab to the tabview needs to move from AppDelegate to SceneDelegate. The code will now be here:

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        let tabBarController = window?.rootViewController as? UITabBarController
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: "NavController")
        vc.tabBarItem = UITabBarItem(tabBarSystemItem: .topRated, tag: 1)
        tabBarController?.viewControllers?.append(vc)
        guard let _ = (scene as? UIWindowScene) else { return }
    }

Very helpful, thanks!