The original BSD is based on Unix so you could say it's "true Unix", but modern BSD systems has modified the source code so much that almost every code is now more different original Unix so you could say it's "Unix-like".
Illumos in the other hand is actually true Unix as it's based on Solaris which is based on Unix System V.
UNIX only has vague meaning. BSD is true UNIX, Darwin is butchered UNIX, Windows has POSIX compatibility enviroment(cygwin), Linux is POSIX.
That was my point. Also BSD is not true Unix, it is Unix-like. Only Unix is Unix.
The original BSD is based on Unix so you could say it's "true Unix", but modern BSD systems has modified the source code so much that almost every code is now more different original Unix so you could say it's "Unix-like".
Illumos in the other hand is actually true Unix as it's based on Solaris which is based on Unix System V.
MacOS is UNIX certified https://www.opengroup.org/openbrand/register/