The React team has avoided blessing any specific libraries, beyond things like Babel for JSX transformation.

React-Router is not an "official" library. As far as I know, neither is React-Navigation.

That said, I also don't know much about the ins and outs of React Native, so there _may_ be some semi-official-ish overlap between React-Navigation and React Native.

(Also, this totally causes an abbreviation clash, as "RN" now has multiple meanings. Oops.)