#include <QApplication>
#include <QComboBox>
#include <QGraphicsProxyWidget>
#include <QGraphicsView>

int main(int argc, char *argv[]) {
    auto app = new QApplication(argc, argv);
    app->setStyleSheet("QLabel{color:red;}");

    auto view = new QGraphicsView();
    auto scene = new QGraphicsScene(view);
    view->setScene(scene);
    view->showMaximized();

    auto proxy = new QGraphicsProxyWidget();
    auto combo = new QComboBox();
    combo->addItems({ "A", "B", "C" });
    proxy->setWidget(combo);

    scene->addItem(proxy);

    return app->exec();
}