You're intentionally stepping around my arguments. Sure, it has no cost for Mac owners, but the ISO is free to download, and Hackintoshes are very much a thing. Again: if we use your definition, then
anything requiring paid hardware cannot, by definition, be free. Which is absurd to suggest. No one I've met claims that free macOS exclusive software isn't actually free. Why is the OS any different.
Violating the EULA that Apple makes you agree to during install (by making a Hackintosh), while a tortuous action, is not necessarily illegal, and it doesn't cost money.