For example, if you use FreeTube with SponsorBlock to improve your privacy and block ads, in fact you are sending to Cloudflare 100% of your YouTube watch history, and to SponsorBlock ("sponsor.ajay.io").
With Piped instances it's even worse, essentially escaping Google's tracking just to give our data to random strangers.
If you are worried, just run a second Chrome session with NordVPN and uBlock Origin in a loose jurisdiction and browse YouTube unlogged.
It's easy, simple, and you have the benefits of an audited platform and that reasonably legally confirm they don't store logs unless the court forced them: "we never log their activity unless ordered by a court never log their activity unless ordered by a court", but for that, the court has to find you as a user, which can be very complicated in practice.
So much better than random strangers.