It's not, but the DarkPlaces engine [0] reimplements many, if not all, of the realtime shadow features and has an X64 Mac build (but no ARM build, as far as I'm aware), and is still getting active contributions on its Github repo[1].

[0]: https://icculus.org/twilight/darkplaces/index.html

[1]: https://github.com/DarkPlacesEngine/darkplaces