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.
"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".