Is Building Yocto project on a POSIX system, a desire for the Yocto project? It would allow support on all bsd UNIX’s including macOS
Making OE itself work isn't rocket science - fix a few Linuxisms in bitbake, port pseudo to macOS.
The hard bit is then convincing the hundred-odd recipes that are often Linux-centric if not Linux specific to build under something that isn't Linux. My ross/darwin branch (from before the security changes) has a patch to gmp as 'echo' has different semantics. unlink() has different error codes between macOS and Linux. There's a very long tail of differences that will need patching and testing.
But if this is something you care about, patches welcome!