App Interface Guideline: Performance — Virtualize Long Lists. Keywords: FlatList SectionList virtualization. Platform: iOS/Android/React Native. Description: Use FlatList/SectionList for lists over ~50 items. Do: Use keyExtractor and initialNumToRender appropriately. Don't: Render hundreds of items with ScrollView. Good Example: <FlatList data={items} renderItem={...} />. Bad Example: <ScrollView>{items.map(renderItem)}</ScrollView>. Severity: High.