Figs parent
I do not understand why Google doesn't just explicitly permit people who pay for premium to use yt-dlp or other tools to watch YouTube however the fuck they want. Put that in your terms, Google -- so people aren't afraid they'll lose their GMail because they wanted to watch a video -- and you'll get more paying customers...
Seriously, there's even that "Download" button but it goes to some weird janky browser-local storage instead of just giving me a damn file.
(I don't think they'd realistically get more paying customers, but I would appreciate it anyway.)
Youtube used to have working download buttons on any video that the uploader licenced as creative commons.
The version of their app that used their V2 API also allowed downloading any video (local to the app, not easily copied) or even setting it to auto-download all of your subscription feed as videos came out.