AppDelegate.swift

import Flutter
import FlutterPluginRegistrant

@UIApplicationMain
class AppDelegate: FlutterAppDelegate {
    
    // other AppDelegate properties
    
    // create multiple Flutter Engines
    lazy var passcodeFlutterEngine = FlutterEngine(name: "my flutter engine")
    lazy var informationTabFlutterEngine = FlutterEngine(name: "my flutter engine 2")
    lazy var qrcodeFlutterEngine = FlutterEngine(name: "my flutter engine 3")
    
    override func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        flutterEngine.run()
        informationTabFlutterEngine.run()
        qrcodeFlutterEngine.run()
        
        // other app initializations
        
        // need to register all packages used in Flutter with each instance of FlutterEngine
        GeneratedPluginRegistrant.register(with: self.flutterEngine)
        GeneratedPluginRegistrant.register(with: self.informationTabFlutterEngine)
        GeneratedPluginRegistrant.register(with: self.qrcodeFlutterEngine)
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }
}