Here is an example code to show the Qdialog.

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    d = new QDialog(this, Qt::FramlessWindowHint | Qt::WindowStaysOnTopHint);
}

MainWindow::~MainWindow()
{
    delete ui;
}


void MainWindow::on_pushButton_clicked()
{
    d->exec();
}

The QDialog works perfectly on x86 host PC, but my embedded Linux works incomplete.

1. The QDialog default position should locate at centered on top of the parent's top-level widget.
   But QDialog in Wayland shows on a random position. Even I try to use "move" to assign a specific position, it doesn't work.
2. The modal dialog can work. The parent is blocked. But there is no darkness effect on parent widget.