I think we should kind of wait for the dust to settle on #29546 but I am pretty sure that with the improvements in OpenMP detection in Meson 1.5 mesonbuild/meson#13350, you don't need to set any environment variables and that our macOS installation doc can be simplified.

We may be setting environment variable in our CI as well, this is worth a look if we can remove them.

cc @EmilyXinyi if you feel like working on it at one point.

I guess it's good to note that this is a positive side-effect of moving away from setuptools to Meson: some things just work better out of the box. I am certainly slightly biased but I am personally convinced that the cost of switching was worth it. Future will tell if I was wrong but I am reasonably confident about this 😉.