React Native doesn't abstract mobile frameworks, so you still need to learn it all as far as iOS UIKit and Android SDK (and also learn React Native stuff on top of it).

That said, there is something about coding in mostly one language (javascript) vs 2 or 3 (Objc/Swift/Android) and also have that live app reloading.

In any case, this react stuff is not for beginners and won't make learning mobile platforms easier - you will still need to put in obligatory 10k hours to get good at mobile dev...