there's a bunch of apps you can install on NAS/plex servers like sonarr (TV), radarr (movies), overseerr (request anything) that basically automate it all. There are hundreds, like ones that add subtitles or download user cover art.
overseerr is what you are talking about, its a web interface that lets friends who have access to your plex server request any movie/show/anime. It shows everything new (or old) and users can request the NAS to auto download it. There are tons of admin options like only certain users can do requests, or you can override requests or only allow 1080p downloads or whatever
Thats what I meant though by this stuff makes netflix/HBO/AppleTV/etc obsolete, once you get these apps setup its all automated. I just have to tell overseerr to auto download 4K HDR copies of Knight of the Seven Kingdoms and it'll automatically handle it all for me for past and future seasons, after I configure it to download from a private tracker with my key. There are a ton of 200TB private plex servers hosted in datacenters that are shared between 5-20 users and they each basically contain everything popular ever made.