// pMainMenu = new QMenuBar()
    QAction* pAction = pMainMenu->myAction(); // new QAction
    connect(pAction, &QAction::triggered, this, &MainWindow::openMyWindow);

   // pMainMenu = new QMenuBar()
    QAction* pAction = pMainMenu->myAction(); // new QAction
    connect(pAction, SIGNAL(pAction->triggered(bool)), this, SLOT(openMyWindow()));

connect(pAction, SIGNAL(pAction->triggered(bool)), this, SLOT(openMyWindow(bool)));

QMetaObject::Connection QObject::connect(const QObject *sender, const char *signal,
                                         const QObject *receiver, const char *method,
                                         Qt::ConnectionType type)
{
    ...

    if (method_index_relative < 0) {
        err_method_notfound(receiver, method_arg, "connect");
        err_info_about_objects("connect", sender, receiver);
        return QMetaObject::Connection(nullptr);
    }

    ...
}

MainMenu::MainMenu(QWidget* pMainWindow): QMenuBar(pMainWindow)
{
    pAction = new QAction("text");
}

MainWindow::MainWindow(QWidget* pParent) : QMainWindow(pParent)
{

  pMainMenu = new MainMenu()
  setMenuBar(pMainMenu);

  connect(pAction, SIGNAL(triggered(bool)), this, SLOT(openMyWindow(bool)));

}