Thanks for the reply. I have filed a bug report (FB21371786).

I am running into the same issue -- I believe the problem is the following error log: There is no available Metal device on this system. It seems Xcode Cloud does not use Apple silicon unfortunately and it seems Metal is required to compile a Skybox resource... So I'm not sure how to move forward with this -- I tried to see if there's a way to "pre-compile" a Skybox resource but I haven't figured anything out yet. I'm going to file a Radar.