If you're on iOS, I highly recommend Yattee[1], a free Youtube app with no ads, background playback and sponsor block built-in.

The way they get around App Store restrictions is by claiming that they aren't a Youtube app. They're technically a video-watching app which is supposed to be used with your own personal server. The server API they require, however, is supported by Invidious[2], an open-source, privacy-preserving Youtube front end. If you configure an Invidious instance in settings[3] (you don't have to host your own, there are plenty of them out there), you effectively get access to the entirety of Youtube.

It's not a replacement for the official app by any means, it doesn't have a recommendation feed, it doesn't let you log in with a Google account, so it doesn't sync watch history with your other devices, it doesn't let you cast to Youtube-enabled devices, post comments, scroll through shorts etc, but if you have a playlist or a specific, longer video in mind, it's quite good. It also supports Invidious accounts, which let you manage channel subscriptions.

[1] https://apps.apple.com/us/app/yattee/id1595136629 [2] https://invidious.io/ [3] https://gonzoknows.com/posts/yattee/