After discussion in #qt-lighthouse about current qtwayland behavior It was recommended to make this bug report for the winId() behavior. Currently it returns a qt internal window id instead of some native type (like a wl_surface) in the wayland-egl backend (and likely others).

A quick overview of the issue was that on existing platforms (X11, Windows, Mac) some applications use winId() to get access to a native windowing system surface in order to control rendering of that surface (think VLC preview, in my case OBS preview) outside of QT. And at least for downstream it would be nice if a comparable method could be achieved on wayland.

In other platforms this native window handled appeared to live for the duration of the process where as wayland surfaces might need to be recreated due to structure changes, it was unclear how precisely these handles on other platforms might live. There was also discussion of potentially using other protocol features such as wl_subsurfaces.