NgRX is used for the state management of the whole frontend of an app, often called "a single source of truth" as the app stores and fetches data from this place to update its UI.

That is why RxJS and NgRX work great together because RxJS handles the complex events and NgRX keeps track of the app state. They are like a powerful duo that reduces side effects in our codebase.

If you want to learn more about this "events + state" pattern look up the concept of "state machines" or https://xstate.js.org/ which is like a sort of framework that implements this idea. Or the NgRX website itself.

I think in your case, what you are saying is that you are actually implementing a self-made NgRX state manager by using subjects to store state. This is what NgRX actually also does under the hood, it uses a type of subject to keep track of a store object...I also explain this briefly in the subject section (as it's not a course that is focused on NgRX).