In Scrum, how can I efficiently manage my product backlog if I need to develop both Android and iOS apps with the same features?

We are doing this right now. We have 4 developers, one UX/UI designer, 1 tester and one BA. We do the stories as normal. "As a user I want to do X so that I can achieve Y" With acceptance criteria in the given /when /then format. When a story requires changes to the admin portal, the iOS app and the Android app we create a subtask for each and do them at the same time. The story is not complete until all three tasks are done. Our developers are fairly new to mobile app development so we decided one would specialize in Android, one would focus on iOS and one would focus on the admin portal. The other members of the team work on all. As we got into it we found that it was taking much longer to develop on iOS than on Android so we put the Android developer and another developer on iOS until we caught up. It hasn't taken them long to learn.

I agree with Murray's answer: "When a story requires changes to the admin portal, the iOS app and the Android app we create a subtask for each and do them at the same time. The story is not complete until all three tasks are done." Your team is small enough that you shouldn't have to worry about velocity at the "component team" level, so having a top level Story (with points), and sub-tasks for each component (without points) will work fine. The "teams" velocity will reflect a mix of skill sets but that's typically OK for small teams. But I also agree with Cliff for larger teams.  For "component teams" of 3-5+, I have found it useful to track velocity at the component team level (e.g. IOS, Android, Platform), as well as in aggregate.  (You're bottleneck may be your IOS team.  How can you show that without velocity measured at that level.  Also, one could phrase a user story as, "As an iPhone user...")  In Jira, tracking velocity at the component team level can be a little challenging because sub-tasks don't have a points field out of the box (OOB), and if you add it, you double count with the parent if you're not careful.  You could track velocity in hours at the component team level (OOB in Jira), but who does that? Also, we'd commonly "Clone" (again Jira speak) stories between Android and IOS since generally you'd implement the same feature on both platforms. To your question, having stories exist at the "user level" and managing component work through sub-tasks helps you manage your product backlog because you're managing less moving parts.  And generally, when you're talking with stakeholders, they don't care about Android vs. IOS.   However, the risk is, if you measure velocity at an aggregate team level, and the velocity between your IOS and Android teams is vastly different, you may not be setting expectations correctly as to when features will be released on each platform.