dependencies:
  window_manager: ^0.1.1

dependencies:
  window_manager:
    git:
      url: https://github.com/leanflutter/window_manager.git
      ref: main

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  // Must add this line.
  await windowManager.ensureInitialized();

  // Use it only after calling `hiddenWindowAtLaunch`
  windowManager.waitUntilReadyToShow().then((_) async{
    // Set to frameless window
    await windowManager.setAsFrameless();
    await windowManager.setSize(Size(600, 600));
    await windowManager.setPosition(Offset.zero);
    windowManager.show();
  });

  runApp(MyApp());
}

import 'package:flutter/cupertino.dart';
import 'package:window_manager/window_manager.dart';

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

class _HomePageState extends State<HomePage> with WindowListener {
  @override
  void initState() {
    windowManager.addListener(this);
    super.initState();
  }

  @override
  void dispose() {
    windowManager.removeListener(this);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // ...
  }

  @override
  void onWindowEvent(String eventName) {
    print('[WindowManager] onWindowEvent: $eventName');
  }

  @override
  void onWindowFocus() {
    // do something
  }

  @override
  void onWindowBlur() {
    // do something
  }

  @override
  void onWindowMaximize() {
    // do something
  }

  @override
  void onWindowUnmaximize() {
    // do something
  }

  @override
  void onWindowMinimize() {
    // do something
  }

  @override
  void onWindowRestore() {
    // do something
  }

  @override
  void onWindowResize() {
    // do something
  }

  @override
  void onWindowMove() {
    // do something
  }

  @override
  void onWindowEnterFullScreen() {
    // do something
  }

  @override
  void onWindowLeaveFullScreen() {
    // do something
  }
}

import Cocoa
import FlutterMacOS

@NSApplicationMain
class AppDelegate: FlutterAppDelegate {
  override func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
-    return true
+    return false
  }
}

int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
                      _In_ wchar_t *command_line, _In_ int show_command) {
  // ...

-  window.SetQuitOnClose(true);
+  window.SetQuitOnClose(false);

  // ...

  return EXIT_SUCCESS;
}

import Cocoa
import FlutterMacOS
+import window_manager

class MainFlutterWindow: NSWindow {
    override func awakeFromNib() {
        let flutterViewController = FlutterViewController.init()
        let windowFrame = self.frame
        self.contentViewController = flutterViewController
        self.setFrame(windowFrame, display: true)

        RegisterGeneratedPlugins(registry: flutterViewController)

        super.awakeFromNib()
    }

+    override public func order(_ place: NSWindow.OrderingMode, relativeTo otherWin: Int) {
+        super.order(place, relativeTo: otherWin)
+        hiddenWindowAtLaunch()
+    }
}