The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Mac OS X 10.5 Leopard, Mac OS X 10.6 Snow Leopard and all releases from OS X 10.8 Mountain Lion to macOS 14 Sonoma are UNIX 03 certified
I don’t like MacOS, but it’s actually able to be called UNIX.
I’m surprised you don’t lose Unix certification with crap like case insensitive filesystem defaults.
I don’t want to be like Stack Overflow, but tbh you have some design problems if you rely on case sensitive filesystems.
Both HFS Plus and APFS can have case sensitivity enabled, it’s optional.
Enabling it has had a tendency to break third party Mac software though. Adobe used to be a particularly bad offender there.
Being able to be called Unix just means paying for certification. No more, no less.