1. Create Thread
2. Create in thread object based on QOpenGLWidget
3. in Thread call grab() and take correct picture

I open example hellogl2 and add this sample code in main.cpp before return app.exec();

    QShortcut *shortcutF4 = new QShortcut(QKeySequence(Qt::Key_F4), &mainWindow, nullptr, nullptr, Qt::ApplicationShortcut);
    QObject::connect(shortcutF4, &QShortcut::activated, &mainWindow, [&]()
    {
        qDebug() << "F4";
        auto *t = new std::thread([]()
        {
             GLWidget glWidget;
             glWidget.resize(400,400);
             glWidget.grab().save("grab_hellogl2_in_thread_01.png");
             // change something
             glWidget.setXRotation(60*3);
             glWidget.grab().save("grab_hellogl2_in_thread_02.png");
             // change something
             glWidget.setYRotation(75*4);
             glWidget.grab().save("grab_hellogl2_in_thread_03.png");

        });
        t->join();
    });

    return app.exec();

But I see warning "Attempting to create QWindow-based QOffscreenSurface outside the gui thread. Expect failures."

How to do it correctly?