Newpipe can also download. No need for bloated YouTube-App, Premium subscription or ti hassle with a command line tool (in case CLI's are not your thing).
As also mentioned by others, youtube-dl seems kinda dead. However there is a good fork/successor called "yt-dlp" which, in addition to other nice improvements, also somehow manages to work around the enforced heavy bandwidth limit by YT.
It's just a command-line tool to download audio/video from youtube (and many other sites). You'd need to setup the iPad thing yourself, maybe using something like Plex?
Plex has shifted over time to present their content more prominently. It got to the point that your own media isn't even displayed on the default landing screen. Had to re-teach the kids how to find their movies and whatnot.
I haven't had it running in about a year though, couldn't be bothered after a move.
Jellyfin looks nice. I'll have to give it a go. I am dreading having to set everything up again if I move off of plex, rather than just grab my docker-compose file and get going.