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!
Aside from the FOSS that people love.
I will add something real world. I have Plex and Jellyfin running. Now Plex works fine for the most part but certain codecs when I am watching on iOS just has issues and freezes a lot so I have to use Jellyfin, but the UI in Jellyfin is pretty sparse and not as polished.