Isn't Mac based upon freebsd? I've never used freebsd itself, so I'm not sure what the actual difference is besides ux.
That said, a bunch of FreeBSD userland code and utilities were ported over to make the OS POSIX-ish.
It's probably easiest to think of a Mac as an amalgam of many different influences and operating behaviors, as opposed to a direct descendant of any one particular lineage.
They still have a lot of userland BSD parts. Including the very broken grep from FreeBSD (which is fixed in FreeBSD now IIRC):
$ echo "abcdef" | /usr/bin/grep -o "^..."
abc
def
[0] https://en.wikipedia.org/wiki/Darwin_%28operating_system%29
https://github.com/apple/darwin-xnu/tree/master/bsd
Also, more recently they imported pf from OpenBSD:
https://github.com/apple/darwin-xnu/blob/master/bsd/net/pf.c
Or do you mean that they have recently taken more code from other BSDs than FreeBSD?
The POSIX network stack for example, is now deprecated, and one must use Network.framework for the more up to date features,
"Introducing Network.framework: A modern alternative to Sockets"
https://developer.apple.com/videos/play/wwdc2018/715/
"Optimizing Your App for Today’s Internet"
https://developer.apple.com/videos/play/wwdc2018/714/
Likewise the long term roadmap introduced in Catalina plans to turn macOS into a micro-kernel, by moving all kernel extensions into userspace drivers.
The macOS kernel is derived from what Apple chooses to release as XNU, which is Mach-ish.
There may be confusion due to the fact that Apple used to publish a Darwin iso that you could boot on their ppc machines, but that's been a long time and OSX is still Darwin. If you run uname on a mac it will tell you that it's Darwin.