Expanded Client Areas Not Working for Widgets Application on MacOS

I read the blog post about expanded client areas and safe areas (see link below).

Is this functionality only for QtQuick applications or does it also work in C++ Widget applications?

I tried to implement this in a Widget-based desktop application. I set the hints on the main window, added a label with pixmap to the central widget, and set a grid layout with 0-widget margins on the central widget. When running the application, the pixmap occupies the whole main window, but the application title bar, status bar, etc. are the normal look and feel. Based on the blog, I expected the pixmap image to be the background for the application menubar.

https://www.qt.io/blog/expanded-client-areas-and-safe-areas-in-qt-6.9?utm_source=installer&utm_medium=banner&utm_campaign=installer4Qt69