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” 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.