Window minimizing broken after building QT app with Mac OS High Sierra SDK

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
    //remove native OS-titlebar
    setWindowFlags(Qt::Window | Qt::FramelessWindowHint);
    
    QPushButton* minimizeButton = new QPushButton();
    minimizeButton->setText(QLatin1String("Minimize"));
    connect(minimizeButton, &QPushButton::clicked, this, &QMainWindow::showMinimized);
    
    QPushButton* quitButton = new QPushButton();
    quitButton->setText(QLatin1String("Close"));
    connect(quitButton, &QPushButton::clicked, this, &QMainWindow::close);
    
    QHBoxLayout* layout = new QHBoxLayout();
    layout->addWidget(minimizeButton);
    layout->addWidget(quitButton);
    
    QWidget *centralWidget = new QWidget();
    centralWidget->setLayout(layout);
    setCentralWidget(centralWidget);
}