Redox bills itself as a Unix-like OS. Seems to me Posix compliance, or attempting to get close to it would fall under being "Unix-like".

If they wanted to build a Unix, they’d have said they were building a Unix.

I think you're splitting hairs. If someone is making an OS they claim is "Unix-like", then it isn't unreasonable for someone to expect that the code that compiles and runs on AIX, HP-UX, MacOS, Solaris, and OpenBSD will also compile and run on this new "Unix-like" OS with minimal changes. If they're not going for POSIX compliance, or even getting reasonably close thereto, they're going to have a hard time being "Unix-like" in practice, certifications be damned.

Might be worth reading this: https://en.m.wikipedia.org/wiki/Unix-like

Unix like might also mean the CLI experience.

For example, AmigaDOS and BeOS took some ideas from Unix, without being Unix compatible.

Is windows unix-like because it implemented POSIX via WSL?