Cannot find a user in the dashboard though my anonymous account successes to login

I implemented the authentication by an anonymous account in Firebase Authentication with Flutter.

The signup/login successes, has no errors, and everything works.
However, the dashboard doesn't have a user as below.
May I know the reason?

My code

main.dart

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );

  runApp(MyApp());
}

class MyApp extends StatelessWidget {...}

class MyHomePage extends StatefulWidget {...}

class _MyHomePageState extends State<MyHomePage> {

  @override
  void initState() {
    super.initState();
  }

  void dispose() {
    super.dispose();
    print("dispose");
  }

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<TimerProvider>(
        create: (context) => TimerProvider()..init(),
        child: MainPage()
    );
  }
}

class MainPage extends StatefulWidget {...}

class _MainPageState extends State<MainPage> {...}

providers.dart

class TimerProvider with ChangeNotifier {
  String? uid;

  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  Future init() async {
    try {
      await signupUser();
    } catch(err){
      print('init error: ${err}');
    }
  }

  Future signupUser() async {
    _firebaseAuth.signInAnonymously();
    uid = _firebaseAuth.currentUser?.uid;
    notifyListeners();
  }
  
  ...
}