I've been using Ombi for a while now.
It's an http web app that can run in a container or bare metal, that interfaces nicely with plex/emby/jellyfin, the arrs, and a number of different notification platforms (I just use smtp). Users can be created directly in Ombi, or automatically imported from plex/emby/jellyfin (auth is then handled by the respective service so users use the same credentials for both).
Users can request new content within specified daily/weekly/monthly limits, view the status of their requests, and report issues with existing content. Requests will be sent to an admin for approval, or individual users can have 'auto approve' enabled for movies, episodes, and/or music. It also provides a nice 'discover' page listing a bunch of genres to look through along with 'popular', 'trending', and 'upcoming' lists of shows/movies.