“unix” not Unix because of the “Unix Like” systems. Not everything IS “UNIX.”
But what about POSIX?
POSIX
POSIX: A Family of IEEE standards for compatibility between operating systems
The Portable Operating System Interface is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. In order to define a level of compatibility, POSIX specifies many aspects of functionality that can be classified as application programming interface, command-line shell, and shell commands. Originally derived from commonly-found Unix APIs, shells, and commands, today many systems conform to the standard – including branded Unix systems, Unix-like systems, and many systems that were historically unrelated to Unix Continued in Wikipedia
| Year started | 1988 |
|---|---|
| Latest version | IEEE Std 1003.1-2024, 2024 |
It is unix as in how Klenix, Google, Coke, Band-Aide, etc., both brand names and colloquial or common usage.
This phenomenon is called genericization, where a brand name becomes synonymous with a general class of products, often losing its trademark protection. Examples include “Kleenex” for tissues and “Aspirin” for pain relievers.
Wikipedia (Also see Wiktionary or similar)
However, today, after writing this, nothing looks right.