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.
Peertube and owncast are Fediverse alternatives to twitch. Peertube less so. I run an owncast server and love streaming to it, but discovery is shit. If you just want to stream, it’s great. If you want to make it a job, stick to twitch