VNC platform plugin (-platform vnc) does not work with certain QML Types

The issue is mainly observed on multimedia-related components. It can be reproduced by QML Camera or QML Video example running with '-platform vnc' argument on either Ubuntu 20 or 22.

For camera example: all control components are visible. But VideoOutput is totally blacked-out even though camera is on.
For video example: everything is blacked-out. No visible GUI whatsoever.

The issue is NOT observed on widget-based multimedia APIs. For example, widget camera and widget video player work perfectly with vnc plugin.

The issue is observed on both Qt5 and Qt6. However, the new VncItem Type in Qt6 works well even with QML Types.