Reality Composer (not Pro) is not included with the newest release of Xcode, and there is no option to download it from developer resources for macOS. The most recent Xcode version that I am aware of that includes Reality Composer for macOS is 14.3.1, however it is incompatible with Sonoma. You can still access it through the "Open Developer Tool" menu. Once you have the app, you can either export the ".rcproject" as ".reality" directly, or incorporate it into a Xcode project, which will automatically convert it during compilation. I hope this is helpful. I still have some existing projects that used this format, so I am presently in the process of phasing out support for it and solely utilizing USDZ instead.

Thanks @matt_novoselov! We tried already, but it does not seem to be called, not in the simulator nor in real Shareplay sessions. Does it work in your case? What about TabletopNetworkSession? Have you managed to access it and any of its features? like processincomingmessage(_:from:) for example ?