FloatingActionButton not working in Flutter app

You did not add onPressed argument to your FloatingActionButton() widget, which is required! try this:

create a custom view widget like this :

import 'package:flutter/material.dart';

class CustomView extends StatelessWidget {
  const CustomView({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Waybill App'),
        centerTitle: true,
      ),
      body: const Center(
        child: Text('Welcome to Waybill Me'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          /*implement your own logic here,
             what do you want to happen when the user taps on this button
            you can do navigating / 
                       showing Dialogs /
                       sending and fetching data /
                       changing the state of the widget ... */
        },
        child: const Text('Tap'),
      ),
    );
  }
}

and now you can easily pass your CustomView widget to wherever you want to use it; for instance, lets change your code to this :

import 'package:flutter/material.dart';
import 'package:stack_overflow_questions/new.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter ShowCase',
      theme: ThemeData(
        primaryColor: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      //pass to the CustomView to the "home:" in here 
      home: const CustomView(),
    );
  }
}