class Widget : public QWidget
{
protected:
    bool event(QEvent *e) override
    {
        if (e->type() == QEvent::WinIdChange) {
            if (const auto win_handle = windowHandle())
                QWindowsWindowFunctions::setHasBorderInFullScreen(win_handle, true);
        }
        return QWidget::event(e);
    }
};

WWidget widget;
widget->setWindowState(Qt::WindowFullScreen);
widget->showMinimized();