The examples use a navigation library that is implemented entirely in JavaScript and it does not currently aim for 100% accuracy for platform gestures and animations. Pure JS navigation is a work in progress with React Native but, in my eyes, it's the ideal end-state (see a post I wrote here for more info: https://blog.expo.io/good-practices-why-you-should-use-javas...), but to get there we need some more powerful low level primitives such as a better gesture API.
Also, I'm curious which examples stood out to you. The "Growler Prowler" app intentionally pushes a screen on top without sharing a navbar, even though this is possible, because this works better for the detail screen. See the beautiful PocketCasts app (https://www.shiftyjelly.com/pocketcasts/) for the design inspiration there.
The examples use a navigation library that is implemented entirely in JavaScript and it does not currently aim for 100% accuracy for platform gestures and animations. Pure JS navigation is a work in progress with React Native but, in my eyes, it's the ideal end-state (see a post I wrote here for more info: https://blog.expo.io/good-practices-why-you-should-use-javas...), but to get there we need some more powerful low level primitives such as a better gesture API.
If you prefer to trade-off customizability for platform-specific animations, you can use NavigatorIOS with Expo/CRNA - https://facebook.github.io/react-native/docs/navigatorios.ht.... If you eject, you can use a library like react-native-navigation (https://github.com/wix/react-native-navigation) which bridges the native navigation APIs, or an upcoming library from Airbnb which they use in their app.
Also, I'm curious which examples stood out to you. The "Growler Prowler" app intentionally pushes a screen on top without sharing a navbar, even though this is possible, because this works better for the detail screen. See the beautiful PocketCasts app (https://www.shiftyjelly.com/pocketcasts/) for the design inspiration there.
Hope that helps!