I have seen various questions about the same topic, and realized that 'currentUser' does not go with future after the update in FirebaseAuth

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  Future<void> _logout() async {
    try {
      await FirebaseAuth.instance.signOut();
    } catch (e) {
      print(e.toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Phone Auth Demo"),
        backgroundColor: Colors.cyan,
      ),
      body: FutureBuilder(
        future: FirebaseAuth.instance.currentUser(),
        builder: (context, snapshot) {
         final firebaseUser = snapshot.data;
          return snapshot.hasData
              ? Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                Text(
                  "SignIn Success