I checked a few files, and a lot of the foundation library have 2007 until 2009 copyright notices. Another random check, CALayer.h and CATransform3D from the Quartz framework, shows terribly limited functionality in comparison to the files on macOS 11.5. The latter comes with 198 frameworks, Airyx has 16, 2 of which don't exist (anymore). Catching up seems an impossible task.