This might sound complicated, but youtube videos come in many shapes, many of them have either video only, or audio only !
the best way to get a full resolution video is to download then combine video and audio !
But before we go there, youtube throttles the speed you download videos at ! so youtube-dl needs patching, an alternative would be yt-dlp (See here)
Making sure things will install with pip correctly
apt install python3-pip
python3 -m pip install --force-reinstall https://github.com/yt-dlp/yt-dlp/archive/master.tar.gz
Now, let us try downloading a video/audio
youtube-dl -F https://www.youtube.com/watch?v=mUvrLxaSolc
Now, to combine them without re-encoding
ffmpeg -i ao.webm -i vo.webm -c:v copy -c:a copy output.webm
But remember when you download,
Only VP8 or VP9 or AV1 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM.