Can I block youtube ads with a transparent proxy like squid ?

I haven't tried that, so I'm not entirely sure. I just focused on the easy methods that most people will gravitate towards.

Try it and let us know what you find!

What about a self-hosted youtube auto-downloading queue list ? I’m fine with .mp4 files !

Sounds like yt-dlp. Lots of people use that to get around ads, and also for data hoarding.

I think it is extremely hard because they are served from the same servers (technically, ads are YouTube videos)

And if the logic on the client isn't removed, it will hang waiting for the ad