I think you're not grasping the difference of how Apple is structured compared to most companies, and why I made the comment I did, which is completely verifiable.
Apple slices up departments by function, not by product, which is why there are organizations under Tim Cook such as Software Engineering, Hardware Engineering, Internet Services, etc. Everyone and no one is responsible for shipping all the products as a result of this structure. Software Engineering in particular is responsible for all of the operating systems that powers Apple hardware.
Similarly, this is how smaller departments under each SVP/C-level org are subdivided, and so on to the team level. Each team may be responsible for a particular product, which includes all the experiences for that product across operating systems. There is no single engineer responsible for just macOS/iOS/tvOS/watchOS. Everyone is responsible for everything, and similarly no one is responsible for anything.
Apple's structure is unique compared to other companies, and contrary to how most are run, which probably contributes to your confusion.