戻るボタンが表示されなかったコードは下記

class View1 extends StatelessWidget {
  const View1({Key key}) : super(key: key);
 
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "View1",
      home: Scaffold(
        appBar: AppBar(title: Text('View2'),),
        body: Center(child: Text('View2'),),
        floatingActionButton: ElevatedButton(onPressed: () =>
            Navigator.push(context,
                MaterialPageRoute(builder: (context) => View2()
                )
            ),
        ),
      ),
    );
  }
}
 
class View2 extends StatelessWidget {
  const View2({Key key}) : super(key: key);
 
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "View1",
      home: Scaffold(
        appBar: AppBar(title: Text('View2'),),
        body: Center(child: Text('View2'),),
      ),
    );
  }
}