The following code shows a broken UI on Plasma Wayland

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    auto model = new QStandardItemModel;

    for (int i=0; i < 20; ++i) {
        auto item = new QStandardItem(QString::number(i));
        model->appendRow(item);
    }

    auto list = new QListView(this);
    list->setModel(model);
    auto video = new QVideoWidget(list);
    setCentralWidget(list);
} 

The ListView doesn't update on scrolling. On X11 this works fine.

The cause is the following:

In https://codebrowser.dev/qt6/qtbase/src/widgets/kernel/qwindowcontainer.cpp.html#78 winId() is called on the listview, i.e. not a toplevel window. On Wayland this creates a subsurface, which causes this kind of UI glitches. This is a relatively well-known problem.

Qt is built from 6.6 branch. qtbase 1f0a31d6a6113e92f561fb9172580b5f35147450, qtmultimedia 0c496a16accde6e85a224604eec867a403b9597b