Instantiating view controller from AppDelegate - view controller code runs but doesn't show on screen

This is the code in my AppDelegate that is meant to run after a user successfully authenticates with Google:

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
        print("User Email: \( ?? "No Email")")
        let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
        let homeViewController = mainStoryboard.instantiateViewController(withIdentifier: Constants.Storyboard.tabBarController)
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window?.rootViewController = homeViewController

I can tell by the console that the code in my homeViewController is being run after the user authenticates. However, the homeViewController is not being shown on screen. Is there something else I need to add? Perhaps in the SceneDelegate?

Any guidance is much appreciated!

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