There is Spotube which does that, just not on IOS

Yes

There is no free ad free Spotify on IOS to my knowledge. I recommend Brave browser for ad free YT/YTM/Soundcloud with offline playback. Or Yattee for just YouTube. Another option is the Swisscows search engine which has a integrated ad free music (probably also uses ytm)

Libresprite is a Fork that has a flatpak for a precompiled free version

While it doesn’t use the activity pub it still functions similarly so maybe that’s why it’s listed with the others

The thing most people get wrong is privacy friendly =! private. If you say something publicly (on the internet) you can assume it will stay for ever, if not directly then via some sort of archive. The privacy part of Lemmy/Mastodon is them not collecting data on what you look at to sell it. If you want something private then don’t use Social Media, because what you say publicly will stay public.

I think the issue people have is that threads is way bigger than all Mastodon instances and that they could having control over Mastodon because of the amount of content coming from threads vs the actual Mastodon instances