I’ll start by plugging Harvard’s free courses catalog as well as Udemy
Edit: Gonna add 2 more I remembered-
Blender - I wish I had more time to learn it, but I did start the infamous “Donut Tutorial” once!
Watch Cartoons Online - Lots of good older stuff!
It’s Plex but free and without a central login server handled by a third party
It’s also got a few fewer/not as functional features and no live TV (whoopty do?)
The Arr Suite are what you’re looking for to find content, works with either Plex or Jelly in (or others)
JF does support live TV (and radio now it seems)
https://jellyfin.org/docs/general/server/live-tv/