To certify any version of macOS as UNIX, the security had to be significantly altered (disabling SIP) among a few other things. This is why what is shipped is not what is certified as UNIX. You can /make/ it match what is certified as an administrator, but that would be inadvisable.
EDIT: And really, UNIX certification means nothing except to potentially government agencies and people who don't understand what UNIX and/or UNIX certification is. Or why being "certified UNIX" is generally meaningless: see the BSDs, which are much closer to "UNIX" origins than macOS will ever be.
Or Windows, which is frankly just has better architected internals and abandons legacy UNIX ;-)
https://www.osnews.com/story/141633/apples-macos-unix-certif...
EDIT: And really, UNIX certification means nothing except to potentially government agencies and people who don't understand what UNIX and/or UNIX certification is. Or why being "certified UNIX" is generally meaningless: see the BSDs, which are much closer to "UNIX" origins than macOS will ever be.
Or Windows, which is frankly just has better architected internals and abandons legacy UNIX ;-)