In the earlier days of OS X this was true. A port from one to the other was somewhat trivial. However, Apple has done Apple things and tried to invent their own gaming library API after killing off OpenGL support on Macs and they’ve probably been up to some other buggery since then as well. Porting to Mac is probably equally as difficult from Windows now as Linux, and Linux has overtaken them on number of people who are playing on Steam.
Games have never been “trivial” to port to Mac, why do you think there are so few games that have been ported? Unless you write it for macOS, it’s just not easy or even worth it to port, has been since the Apple II days.
I meant the trivial portion would be porting back and forth between linux and early Mac OSX, making it a two-for-one proposition (though back then a lot of companies still chose not to do the linux port).
They still have some pretty old version of OpenGL and Metal was a bit before Vulkan, so it’s sort of a lightning vs USB C situation.
I don’t believe that it was easy. Since it started macOS was based on BSD, not Linux, which is quite different. They also use different types of binaries and the similarities between kernels should end beyond the BSD compatibility layer. See https://wiki.freebsd.org/Myths#FreeBSD_is_Just_macOS_Without_the_Good_Bits
