Apple no longer allow use of Objective C garbage collection on the MacOS App Store (it was never supported on iOS). This doesn't effect third-party garbage collection and there's no requirement for third-party languages to use ARC (it wouldn't be practical for most of them, anyway, though there is an AOT-compiled Ruby that uses it).
Thank you!
You don't have to use ARC. You can reference count manually if you like. What you can't do is use the old garbage collection (which was only ever available on OS X).
And in fact you _can_ still use the old garbage collection if you really want to; you just won't be able to submit new apps to the OS X app store.