Why is WillPopScope widget not working in my flutter code?

I’m using this function on my custom button to go back one screen, but onWillPop callback is never called

  static Future<bool> back(BuildContext context) async {
    if (Navigator.of(context).canPop()) {
      return Navigator.of(context).pop();
    } else {
      await SystemNavigator.pop();
      return true;
    }
  }