You're a G

Note that YouTube's ToS doesn't allow this either, be aware what you're potentially getting into by releasing a tool that rips music from there.

Uploaders can choose a video license. Since there is no download button for those videos, I've always wondered if that is a creative commons' violation and therefore Youtube should run into the same legal issue that StackOverflow currently is (ctrl+f "violat" https://meta.stackexchange.com/questions/401324/announcing-a...), namely that this terminated google's (but nobody else's) license to use the video under these creative commons terms

All Spotify sees is bytes going to your computer. What happens to those bytes afterward is your own business.