Retain/Release methods would be for manual reference counting, as is traditional in Obj-C/Cocoa.
ARC is a compiler trick in the clang objective-c and swift compilers-- essentially injecting the appropriate retain/release calls for you. You won't get that for free in Go (because, again, it's a compiler feature-- compiled ObjC/Swift code is still calling retain/release just like you would manually), but I'd expect some integration with Go's memory management system so you're not having to make those calls manually. (It looks like that is not here in this particular release, though-- they have retain/release calls in some of their examples.)
Objective-C garbage collection is not a thing any more, and hasn't been for quite some time. Deprecated back in macOS 10.8, and outright removed in more recent versions of the runtime (it was never available on iOS, and was taken out sometime around macOS 10.12 on desktop).
Do the BridgeSupport files annotate whether you own returned objects and need to release them? Sprinkling in runtime.SetFinalizer calls based on ownership would be slightly nicer than exposing release/retain.
ARC is a compiler trick in the clang objective-c and swift compilers-- essentially injecting the appropriate retain/release calls for you. You won't get that for free in Go (because, again, it's a compiler feature-- compiled ObjC/Swift code is still calling retain/release just like you would manually), but I'd expect some integration with Go's memory management system so you're not having to make those calls manually. (It looks like that is not here in this particular release, though-- they have retain/release calls in some of their examples.)
Objective-C garbage collection is not a thing any more, and hasn't been for quite some time. Deprecated back in macOS 10.8, and outright removed in more recent versions of the runtime (it was never available on iOS, and was taken out sometime around macOS 10.12 on desktop).