With Youtube making everything possible to block third-party clients and adblockers to keep you at their bloated site, there are alternatives still available. At the time of writing this, you can browse Indivious or Piped and they’re good alternatives.

On the other hand, you can watch YT on your video player mpv using yt-dlp to extract the video from its url. That simple:

mpv --ytdl-format=bestvideo+bestaudio [url]
# or
yt-dlp -f bestvideo+bestaudio [url] -g | xargs mpv

Enjoy!