Apple specifically compiles OpenMP support out of their builds of clang, so that's never been an easy solution on macOS. Even worse if you want to run on other Apple platforms where an external compiler can't be used.

In practice the software I’ve worked on has typically been engineering/scientific. Back in older pre-ARM days that meant Intel compiler toolchain on all platforms.

Iirc. you just need the openMP libraries from a compatible version of clang.