The new approach of using a Window{} and a QQmlApplicationEngine sets up some more non-visual stuff, but is missing some of the setup done in QQuickView. Specifically, setting an incubation controller to allow asynchronous loading.

int main(int argc, char* argv[])
{
    QGuiApplication gapp(argc, argv);
    QQmlApplicationEngine eng("test.qml");
    qDebug() << &eng << eng.incubationController();
    return gapp.exec();
}