LibreTube - uses Piped as video source by default. Subscriptions and playlists can be created, all without actually interacting with YouTube.
Clipious - uses Invidious as the video source. Also allows for subscribing and accounts. Lesser known client
NewPipe - Gets the source directly from YT. Allows for subscribing and creating playlists
Additionally, there’s also ReVanced that lets you patch the regular YT app to include useful features.
Might be a dumb question but why not just use Piped?
Well, you still need a client if you’re on mobile. I’m not going to watch my video essays through a browser if I can do it through an app. I use libretube which ends up being Piped under the hood, it’s just smoother.
I also used to use revanced because it allowed me to keep a few public playlists up to date (something you can only do by interfacing with Youtube). People have their reasons for things.
This is, in fact, a dumb question