React Native library was announced at Facebook in 2015. Since then, a lot of mobile applications shifted base from being native mobile applications to React Native. In 2014, Facebook F8 applications were built using native code before they rewrote their iOS build to React Native in 2015. And now social network giants like Instagram, Airbnb and some parts of Facebook run on React Native.
For backend, we use Firebase and Rails Backend. Firebase is a powerful platform for backend where it has databases in real-time with security rules. It has Authentication Services, Storage Services (where it provides secure upload and downloads), Firebase Cloud Messaging where you can trigger notifications for a user and it has Cloud Functions where you can add a few logics and remove the weight of code in the mobile app. Many famous applications like Sky Scanner, Pic Collage have successfully implemented this for their mobile applications - this is actually one place for everything. Rails Backend is super fast in both performance & development, and it is constantly improving technology.