Apple introduced Dark mode in macOS 10.14 Mojave, and Microsoft also started implementing it in Windows the same year (2018).
ARCHICAD currently works when the Operating System is turned to Dark Mode, but doesn't have a dark theme yet. This change could be quite development-resource heavy (as the engine of ARCHICAD’s UI is not ready for having 2 different representations, so it would require a complete overhaul), and could also take away time from functional developments in favour of a cosmetic upgrade.
PS.: I found other similar polls but I wanted to get more specific than those. I link them here for reference (I personally like the mock-up of Emil Meijer):
Black/Dark theme option for UIDark GUI themeDark scheme