my friends aren't on it. Plex has the cool sharing of media libraries thing with friends so I can see a bunch of different friend's libraries at once. Not sure if jellyfin has that. And if it does, I'd still have to convince all my friends to move their libraries to jellyfin from plex. And

Jellyfin uses a different user management system than Plex does because there's no "central service" that users register an account to. Instead Jellyfin expects administrators to manage users of their own server. As the administrator of your server you can add or delete users, modify their permissions and set some basic access controls, lock them out, etc. In your case you would provision user accounts on your Jellyfin server for your friends and provide credentials to them.

the UI isn't as good. It's not as pretty, it's kind of boring.

Agreed, but it's very easy to either customize the theme yourself since it's just CSS, or find a theme that better suites your taste.

Hope that clears somethings up for you.

Jellyfin is a decent alternative to Plex for sure. My bigger issue is with Clients. They sort of vary in quality from things like the Roku client crashing all the time, to there not even being an official Apple TV client. I would still prefer Jellyfin over $70/yr or $750 one off lol