I may have more to say about RxJS some other day, but it's something I've been learning since switching jobs at Google late last year to work on a pretty large Angular app. I found it to be a steep learning curve with RxJS and Observables and functional reactive programming in general, but in this case learning RxJS is exacerbated by a lack of good, comprehensive documentation.
However, I did learn that the RxJS team has put together a pretty comprehensive set of docs for RxJS 6. For whatever the reason, they are located at https://rxjs-dev.firebaseapp.com/.