what do you mean exactly? like is macOS compliant with the unix and or posix spec? or whether the day to day interaction with the operating system feels UNIXy and to what extend it follows the kiss principle?

MacOS is quite unixy - however it is pet roadkill for developers.

• Outdated GNU Tools because Apple hates open source
• No customizability (no powertools!)
• If you think Windows forced choice is bad, you’re in for a whole new world of hurt

See more: https://linuxreviews.org/Macs_%26_MacOS:_Greener_Grass%3F

MacOS is legally certified as Unix as far as I know.