Apple does not allow to use their SDK on non-Apple hardware. So if you need to use MacOS headers and libraries, the hardware where the compiler runs must be from Apple. Apple has no problem if you run Linux on that and cross-compile from it to Mac.

At work we could not for that reason use the same compilation server setup to cross-compile for Linux, MacOS, Windows and ended up with a separated MacPro box for the compilation farm.

EDIT: cross-compilation from Windows works after one gets Windows SDK and Visual Studio libraries (the later is not free, but free alternatives often are sufficient). The biggest headache is that Windows headers assume a case-insensitive file system and includes, for example, windows.h when the file is Windows.h. One can either use case-insensitive mount option for ext4 or symlink relevant files to the proper case.