StreamProvider: Error: Could not find the correct Provider<User> above this App Widget

I'm using StreamProvider from the provider package for auth functionality in my flutter-firebase app, just like it is explained in this tutorial https://www.youtube.com/watch?v=j_SJ7XmT2MM&list=PL4cUxeGkcC9j--TKIdkb3ISfRbJeJYQwC&index=9.

When trying to run my app, I get an error message, with a suggestion how to do it correctly, but my code IS written in the way that is suggested.

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(FirebaseWrapper());
  runApp(App());
}

class FirebaseWrapper extends StatelessWidget {
  // Create the initialization Future outside of build():
  final Future<FirebaseApp> _initialization = Firebase.initializeApp();
  // final Future<void> _initSharedPrefs = SharedPrefsHelper().initSharedPrefsInstance();

  @override
  Widget build(BuildContext context) {
    SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
    return FutureBuilder(
      // from: https://firebase.flutter.dev/docs/overview/#initializing-flutterfire
      future: _initialization,
      // future: Future.wait([_initialization, _initSharedPrefs]),
      builder: (context, snapshot) {
        if (snapshot.hasError) return ErrorPage(); //TODO better error pages
        if (snapshot.connectionState == ConnectionState.done) return FirebaseAuthWrapper();
        return Loading(); //waiting
      },
    );
  }
}

class FirebaseAuthWrapper extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamProvider<User>.value(
      value: Auth().userStream,
      initialData: null,
      child: App(),
    );
  }
}

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    print('yeet');

    return MaterialApp(
      key: UniqueKey(),
      title: 'Wanderapp',
      theme: ThemeData(primarySwatch: Colors.blue),
      initialRoute: (user == null) ? '/signIn' : '/',
      routes: (user == null)
          ? {
              '/signIn': (context) => SignIn(),
              '/register': (context) => Register(),
              // '/forgotPassword': (context) => ForgotPassword(),
            }
          : {
              '/': (context) => Home(),
              //...
            },
    );
  }
}

the error message:

Error: Could not find the correct Provider<User> above this App Widget

This happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:

- You added a new provider in your `main.dart` and performed a hot-reload.
  To fix, perform a hot-restart.

- The provider you are trying to read is in a different route.

  Providers are "scoped". So if you insert of provider inside a route, then
  other routes will not be able to access that provider.

- You used a `BuildContext` that is an ancestor of the provider you are trying to read.

  Make sure that App is under your MultiProvider/Provider<User>.
  This usually happens when you are creating a provider and trying to read it immediately.

  For example, instead of:

  ```
  Widget build(BuildContext context) {
    return Provider<Example>(
      create: (_) => Example(),
      // Will throw a ProviderNotFoundError, because `context` is associated
      // to the widget that is the parent of `Provider<Example>`
      child: Text(context.watch<Example>()),
    ),
  }
  ```

  consider using `builder` like so:

  ```
  Widget build(BuildContext context) {
    return Provider<Example>(
      create: (_) => Example(),
      // we use `builder` to obtain a new `BuildContext` that has access to the provider
      builder: (context) {
        // No longer throws
        return Text(context.watch<Example>()),
      }
    ),
  }
  ```

I'm user the same "User" class from Firebase for StreamProvider and Provider.of, the hierarchy/scope also seems to be correct in my code, but it doesn't work. Does anyone know what my mistake is? Thank you very much.