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.
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.