I posted my original comment based off my pre-existing knowledge, but here's a more in-depth explanation of the macOS and FreeBSD situation (which aligns with my understanding):
Essentially, macOS was indeed based on NeXTSTEP originally, but over the years they copied quite a bit of BSD code over (mostly FreeBSD I think). I don't think the Unixy parts of the original NeXTSTEP survives much in modern macOS.
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I posted my original comment based off my pre-existing knowledge, but here's a more in-depth explanation of the macOS and FreeBSD situation (which aligns with my understanding):
https://www.reddit.com/r/freebsd/comments/1g07sdm/comment/lr...
Essentially, macOS was indeed based on NeXTSTEP originally, but over the years they copied quite a bit of BSD code over (mostly FreeBSD I think). I don't think the Unixy parts of the original NeXTSTEP survives much in modern macOS.