So we've had our game live on Arcade for quite some time now, and have had code using Unity's Job System and Burst compiler working long before. At some point, I'm not totally sure when, but only our macOS build seems to not be using Burst, while iOS and tvOS, the editor, and macOS builds without an Xcode project are fine. There's no unusual output that I can see that would indicate a problem, half the time Xcode doesn't seem to get any input from the build but I don't think that's related or affects anything else.
I've built it from my M1 MBP on 12.2, and my Windows 10 desktop. I've tried using Mono or IL2CPP as backend. I've gone through almost every version of Burst. Xcode 13.4.1 and 13.2.1 Unity 2020.3.35, 2020.3.37, 2021.3.8, and I just tried 2019.4.40. Most of these tests were done on a clean repro project.
I've posted on the Unity forums and reported it as a bug with the repro project, I've had no response on either. I'm running out of ideas here, happy to provide any extra info I can.