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.
GrayJay doesn’t cast to Chromecast, it uses F-Cast instead which isn’t on every platform.
Well I was able to cast on Chromecast. But it was a little unstable.