Alt text: meme with the 'Always has been' format Linux, MacOS, OpenBSD and ChromeOS logos on top of the Earth The first astronaut says 'Wait, it's all Unix?' A Windows logo, on top of the second astronaut. The second astronaut says 'Always has been' and points a gun to the first astronaut.
MacOS was not Unix based until OSX (10). MacOS 9 and prior were based on the classic Macintosh kernel.
"macOS" is not the same as "Mac OS"!
"Mac OS X" was rebranded to "macOS" (or rather, "macOS" is the successor to "Mac OS X", but really just is the same but newer, the "upgrade" was just like any other update between Mac OS X versions afaik), and "Mac OS 9" does not belong to "macOS".
IIRC Mac OS X was changed to OS X before it was changed to macOS. Not that it matters here
Edit: 10.0 to 10.7 were Mac OS X, 10.8 to 10.11 was OS X, 10.12 and later macOS.
Dove into that some time ago.
NeXTSTEP was made by Steve Jobs after quitting Apple, awesome Software anr Unix based, but the hardware was overprices.
Then Mac bought NeXTSTEP back and made their first good MacOS on the Unix base, which is what they use to this day.
Afaik they also use the same Kernel and and some more in all devices.