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.
But I don’t have Roku
Web Video Caster can cast to a large number of devices, Chromecast included. It has a lot of companion apps too on several smart TV platforms, all for the sake of getting your media played back on another device.