FWIW, OpenGL on macOS is deprecated, not removed. This means they ship an ancient version and won't provide support.

I messed around for an hour or so, and managed to get it to compile fully on my older macOS 10.12 system. It seems to mostly work, but snis_client just throws up a black screen. Clicking on certain regions on the bottom left/right corners does emit a sound effect, so it is running. Further investigation is in order! I'll submit patches if I figure out some nice fixes, of course.