delegate.swift

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate, OrientationDelegate {
    
    var lastNotificationData: [AnyHashable: Any]?
    
    var isChannelInitialized = false

    ...

    override func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
        
        
        let userInfo = response.notification.request.content.userInfo
        
        // Send the notification data to Flutter
        if(!isChannelInitialized) {
            // If the channel isn't initialized yet, save the notification data
            self.lastNotificationData = userInfo
        } else if let controller = (UIApplication.shared.delegate as? AppDelegate)?.window?.rootViewController as? FlutterViewController {
            let channel = FlutterMethodChannel(name: "com.helloinside.glucose/notification", binaryMessenger: controller.binaryMessenger)
            channel.invokeMethod("onNotificationTap", arguments: userInfo) { result in
                print("Method call result: \(result)")
            }
        } else {
            // If we can't get the FlutterViewController, save the notification data
            self.lastNotificationData = userInfo
        }
        completionHandler()
        
}