Lest we despair, macOS was based on FreeBSD. Also, lest we become overly enthusiastic, macOS is about the only successful desktop based on FreeBSD (apologies to y’all Dragonfly folks).
I wish there was more diversity in this regard but I think it’s an unfortunate instance of collateral damage of the GPL vs permissive licensing wars.
Writing something like 'MacOS is based on FreeBSD' implies a situation more like Sony's OrbisOS, which isn't the case with MacOS.
Can you share some source of your statement?
It won't be that many years before I imagine we'll start seeing people asking to cite how the next forms of ChromeOS or Android were related to Linux.
And to clarify my example, Fuchsia is set to be a Linux-less functional rebuild of Android, but it'd be a bit myopic to point out that "there's no Linux in Fuchsia". It's like saying there's no Steve Jobs in any Apple products created after his death. Less perhaps, but not none.
https://en.wikipedia.org/wiki/Darwin_(operating_system)
There's probably very little commonality left nowadays though. However, if you go back to the earlier days (Panther, Tiger, Leopard) and look at the release notes of Mac OS at the time, and the release notes of the contemporary FreeBSD version of the time, you'll see very similar text: I remember word-for-word paragraphs about things like NFS fixes in both.