Free and open-source YouTube clients w/ no ads

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.