There is one guy (Parafin) who single-handledly maintains Mac OS builds. It feels like he is getting more and more annoyed by Apple periodical backstabbing (no more OpenCL, use Metal. No more x86, use ARM. Etc.).
There is no plan to actively drive a migration. People are just tired of Mac OS discrepancies. If a Clang compilation can handle the cross-plateform oddities, well ok. If not, don’t expect miracles : motivation runs low.
Plus, darktable heavily relies on the Gtk stack, and its interactions with MacOS are already conflictual (font sizes, display color profiles, and that kind of thing).