If your concern is privacy, I've developed this project which routes everything through Tor except for the video file: https://github.com/user234683/youtube-local

There is also this project which is similar but much better, more polished, and with more features than what I have currently, but I haven't tried it to see if it supports a similar kind of selective proxying: https://github.com/omarroth/invidious

Then there's Freetube, which supports proxying but I'm not sure of the details either. It doesn't scrape Youtube itself as far as I know; instead it consults with the main Invidous instance at invidio.us which provides an api: https://github.com/FreeTubeApp/FreeTube