QWindow can't display in QWidget wrapper if top-level QWidget is set Qt::FramelessWindowHint && Qt::WA_TranslucentBackground in the same time.

As a example project: Qt\Examples\Qt-6.6.0\vulkan\hellovulkanwidget.

If belows 2 line was added in Class MainWindow' s construct function, the VulkanWindow won't be shown anymore.

this->setWindowFlag(Qt::FramelessWindowHint);
this->setAttribute(Qt::WA_TranslucentBackground);

This bug can appear with any QWindow wrappered by QWidget.