Android 12和13中，为了保护用户的隐私，系统对后台执行的一些操作进行了限制，导致在ionic5的App后台发送Firebase推送通知时会出现问题。为了解决这个问题，可以按照以下步骤进行操作：

1. 在AndroidManifest.xml文件中添加以下代码：

2. 在App启动时，获取后台任务的授权：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
  // Create channel to show notifications.
  String channelId = getString(R.string.default_notification_channel_id);
  String channelName = getString(R.string.default_notification_channel_name);
  NotificationManager notificationManager =
          getSystemService(NotificationManager.class);
  NotificationChannel channel = new NotificationChannel(channelId,
          channelName,
          NotificationManager.IMPORTANCE_LOW);
  notificationManager.createNotificationChannel(channel);

  // Start the service
  Intent serviceIntent = new Intent(this, MyFirebaseMessagingService.class);
  startForegroundService(serviceIntent);
} else {
  // Start the service
  Intent serviceIntent = new Intent(this, MyFirebaseMessagingService.class);
  startService(serviceIntent);
}

3. 在处理Firebase推送通知的服务类（例如MyFirebaseMessagingService）中，启动前台服务并显示系统级通知：

public class MyFirebaseMessagingService extends FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);
        //处理推送通知

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            String channelId = getString(R.string.default_notification_channel_id);
            NotificationCompat.Builder notificationBuilder =
                    new NotificationCompat.Builder(this, channelId)
                            .setContentTitle(remoteMessage.getNotification().getTitle())
                            .setContentText(remoteMessage.getNotification().getBody())
                            .setPriority(NotificationCompat.PRIORITY_HIGH)
                            .setSmallIcon(R.drawable.ic_notification);

            NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);

            notificationManager.notify(0, notificationBuilder.build());

            Intent intent = new Intent