I already do this. There are several apps for it but I really like Pinchflat because it has metadata settings for Jellyfin.

All I have to do is add a video to a playlist and it gets automatically downloaded. I use it for archival but there's nothing stopping you from making it the only way you consume YouTube content.

Yeah, I download whatever I want to watch and fire up vlc. 0 ads, 0 buffering.

I had a time, when i had frequent internet disconnections, and connection speed was slow in general, so while i had the internet connection, i just downloaded a bunch of videos, to then watch offline. Suprisingly, downloading video even with slow internet is faster than streaming it, despite when streaming it, videos was always buffering. Now i have stable internet and i can just stream videos without the problem, even by using third party app with no ads and without account.

Wait, you think all YouTube content is available in torrents?