You should read the official wiki. https://wiki.freebsd.org/Myths#FreeBSD_is_Just_macOS_Without...

> Darwin - which consists of the XNU kernel, IOkit (a driver model), and POSIX compatibility via a BSD compatibility layer - makes up part of macOS (as well as iOS, tvOS, and others) includes a few subsystems (such as the VFS, process model, and network implementation) from (older versions of) FreeBSD, but is mostly an independent implementation.

The two operating systems do share a lot of code, for example most userland utilities and the C library on macOS are derived from FreeBSD versions.