Facebook app also has huge chunks of platform-native code, it's why they also have things like Litho: https://fblitho.com/

And according to their announcement post Litho is what they are using for their News Feed: https://code.facebook.com/posts/1187475984695956/open-sourci...

So the most critical part of the Facebook app isn't in React Native. How much of those other apps are actually using React Native?