OpenBSD version 7.6 is the latest release of what is very probably the most secure member of the great Unix family. (Although ...
These are uncharted waters for me and there was a substantial choice to be made as to which one, so after reading around the subject I settled on FreeBSD as it seemed the most accessible.
Explainer Apple's latest OS release is the newest member of the Open Group list of officially verified UNIX variants – by quite some margin.