I am trying to prepare a binary update for another computer running FreeBSD.

Unfortunately, that computer’s specifications are too low to perform a buildworld directly on it.
Following the documentation on building FreeBSD on a non-FreeBSD host (building on non freebsd host)

I attempted to run the process on my macOS machine. However, I encountered the following error:

make buildworld TARGET=amd64 TARGET_ARCH=amd64                                
Makefile:127: *** missing separator.  Stop.