Hairsplitting. We all know there was nothing major in macOS 11 justifying it not being an X-os anymore. They just got tired of the naming scheme.

Yep, since 2020 [0]. Or are you being pedantic about OS X vs macOS?

[0] https://en.wikipedia.org/wiki/Apple_M1#Products_that_use_the...

It's a Mac OS X program that runs on post-X macOS.