The short answer
Dynamic Island is not a permanently updating widget. Apps present supported real-time information there through Apple’s Live Activities system. A walking app can use that surface for glanceable progress while a Live Activity is running.
What belongs there?
Keep it compact: current progress, a clear goal state, and enough context to understand the number without opening the app. StepIsland pairs step progress with its companion so the surface still feels like the product instead of a tiny spreadsheet.
What StepIsland is building
StepIsland uses Live Activities to keep daily walking progress close on supported iPhones, with compact and expanded presentations designed around steps, goal progress and the current companion.