IBM won the long game. They secretly acquired Apple, but you weren't meant to know that yet. Not even Tim Cook knows. Big Blue's lawyers will be writing politely to the author of this project, and teaming up with the gutted remains of Nullsoft to sue them for copyright infringement.
I know this was in jest, but had some of Apple’s and IBM’s 1990s plans came to fruition, we could’ve ended up with an operating system capable of running both OS/2 and Taligent (the original planned successor to the classic Mac OS) applications on PowerPC hardware (one of the few parts of the Apple/IBM collaboration that was realized):
I wondered initially if this was a winamp port for older macs.
It requires macOS 13.0 (High Sierra, 2017) or later, which is several releases after it stopped being called OS X. 10.11 (El Capitan, 2015) was the last OS X.
(I personally would accept someone referring to High Sierra as “OS X” because it’s still version 10 of the Macintosh OS, even if Apple dropped that branding a few years earlier.)
Not taking anything away from the project, which looks very cool, but it also probably doesn’t compile on OS X. Looks like minimum macOS version is 13.