[x] Since your genres are being stored directly on the movies, you wouldn't need to track them in a separate slice of state. If you wanted to display all movies of a particular genre on the frontend, you could implement a selector that iterates through the movies slice of state and adds each movie that matches to an array. If you want to grab all movies from a particular genre from the backend, you could pass the genre that you are searching for as a parameter to your server and find all movies where the genre matches.
[x] Similarly, you would then not need a movieGenres slice of state.
[x] If a user can only have one list and you are only ever interacting with your own information (not looking at other users' accounts on netflix), your information about what movies are on the current user's list can be stored in your session slice of state.
[x] Your session slice of state can track all of the information that you need about the current user. I would expand this reducer to track the username and email that you are storing in the database as well as the listMovieIds association that you are tracking. If you need to display all of the movies that are on the current user's list you can then grab the ids of the movies that you need with state.session.listMovieIds and iterate over the array to key in to the appropriate movie in state.entities.movies[listMovieId].