In versions Qt6.7.3, 6.8.2, and 6.9.0beta, when I tried to customise the style of QMenu using QSS, I found that after removing the shadow, there was a residual black background in the bottom right corner, with the larger the rounded corners, the greater the affected area. However, in versions 6.5.3 and 6.5.2, I tested with the same code and this issue did not occur. Through my verification, it is not a problem with my code, but a bug in versions 7.x.x and above, including the new version, and I hope this bug can be resolved in the new version by the officials. Attached are two screenshots from the test, showing the effect clearly. Below is a simple test code:

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QPushButton btn("clicked");

QMenu menu;
menu.setMinimumSize(400, 400);
menu.move(200, 200);
menu.addAction(new QAction("1111111"));
menu.setAttribute(Qt::WA_TranslucentBackground);
menu.setWindowFlags(menu.windowFlags() | Qt::Popup | Qt::NoDropShadowWindowHint|Qt::FramelessWindowHint);
menu.setStyleSheet("QMenu\{border: 2px solid red; border-radius:40px; background-color:black;}");
QObject::connect(&btn, &QPushButton::clicked, [&]() {
menu.exec();
});

btn.show();
return a.exec();
}