I couldn’t find a solution for displaying a snackbar after clicking on an IconButton which is inside the AppBar. The difficulty here is that the appBar() is shifted to an own file/class called myAppBar.dart.

Calling the appBar from a specific view:

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: const PreferredSize(
        preferredSize: Size.fromHeight(50),
        child: **MyAppBar**(
          title: "My Home",
        ),
      ),

AppBar.dart Code:

import 'package:flutter/material.dart';

class MyAppBar extends StatelessWidget {
  const MyAppBar({super.key, required this.title});

  final String title;

  @override
  Widget build(BuildContext context) {
    return AppBar(
      elevation: 0,
      title: Text(title),
      backgroundColor: Color.fromRGBO(72, 75, 80, 1),
      actions: <Widget>[
        Builder(
          builder: (BuildContext context) {
            return IconButton(
              icon: const Icon(
                Icons.refresh,
                color: Colors.white,
                size: 30,
              ),
              onPressed: () {
                //print("success");
                **final snackBar = SnackBar(content: Text('Yay! A SnackBar!'));**
                // *What can I write here??*
              },
            );
          },
        ),
      ],
      centerTitle: true,
      bottom: const PreferredSize(
          preferredSize: Size.fromHeight(10),
          child: Divider(
            thickness: 0.3,
            height: 0,
            color: Color(0xffAEADB2),
          )),
    );
  }
}

The following solution doesn’t work:
Scaffold.of(context).showSnackBar(snackBar);

child: MyAppBar(
          title: "Nik's Home",
          Scaffold.of(context).showSnackBar(snackBar); || **Expected to find ")".**
        ),