Try running on a real device
Try this:
AppDelegate.swift
import UIKit
import Flutter
import Firebase
import FirebaseMessaging
import UserNotifications
@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
    var firebaseToken : String = "";
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    Messaging.messaging().delegate = self;
    FirebaseApp.configure()
    GeneratedPluginRegistrant.register(with: self)
    Messaging.messaging().isAutoInitEnabled = true;
    self.registerForFirebaseNotification(application: application);
    return true;
   // GeneratedPluginRegistrant.register(with: self)
    
  }
   override func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken : Data){
    print("X__APNS: \(String(describing: deviceToken))")
       Messaging.messaging().apnsToken = deviceToken;
    //Messaging.messaging().setAPNSToken(deviceToken, type:MessagingAPNSTokenType.prod )
    }
    
    override func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
        print("X_ERR",error);
    }
    
     func registerForFirebaseNotification(application : UIApplication){
    //    Messaging.messaging().delegate     = self;
        if #available(iOS 10.0, *) {
            //UNUserNotificationCenter.current().delegate = self ;
            let authOpt : UNAuthorizationOptions = [.alert, .badge, .sound];
            UNUserNotificationCenter.current().requestAuthorization(options: authOpt, completionHandler: {_, _ in})
            UNUserNotificationCenter.current().delegate = self ;
        }else{
            let settings : UIUserNotificationSettings = UIUserNotificationSettings(types: [.alert, .badge, .sound], categories: nil)                
            application.registerUserNotificationSettings(settings);
        }
        application.registerForRemoteNotifications();
    }
}
extension AppDelegate : MessagingDelegate{
    func messaging(_messagin : Messaging, didRecieveRegistrationToken fcmToken : String){
        self.firebaseToken = fcmToken;
        print("X__FCM: \(String(describing: fcmToken))")
    }
    func messaging(_messagin : Messaging, didRecieve remoteMessage : Any){
        //self.firebaseToken = fcmToken;
        print("REMOTE__MSG: \(remoteMessage)")
    }
    func application(_ application : UIApplication,didRecieveRemoteNotification uinfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void){
        print("WITH__APN: \(uinfo)")
    }
}
podfile
target 'Runner' do
  use_frameworks!
  use_modular_headers!
#  pod 'FirebaseFirestore', :git => 'https://github.com/invertase/firestore-ios-sdk-frameworks.git', :tag => '7.11.0'
  pod 'Firebase/Auth'
  pod 'Firebase/Analytics'
  pod 'FBSDKLoginKit'
  pod 'Firebase/Messaging'
  flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
end
pubspec.yaml
  cloud_firestore: ^2.0.0
  firebase_auth: ^1.1.2
  firebase_core: ^1.1.0
  firebase_messaging: ^9.1.3
  flutter_local_notifications: ^5.0.0+3
Answered here also