React Native constructs only single UIView by default and draw actual UI using poorly man browser engine using JS. This UI does not "feel native" to user, because it has wrong animation timings, scroll speed, border elevation, missing "native" gestures, etc.
That is certainly true of Flutter, which has its own rendering pipeline. React native, if you create a Button then on iOS you'll get an actual UIButton instance constructed, etc.
It is true for a few components derived from TouchableOpacity like Button, sure. That is NOT true for most other components. You does not have UICollectionView, UINavigationView (only solvable with third-party buggy components), etc.
