Well, usually there is some software and website specially designed for this purpose. One such popular YouTube to MP3 website is
https://listentoyoutube.ch/ You can use it to directly convert YouTube videos to MP3 format.
YouTube2MP3 to download Videos with One-Click.
For YouTube Downloader to MP4, keepvid.digital is the impressive one here. Usually I can't stream 1080 or even some 720p videos,
But I can actually download it and watch at the same time via youtubetomp3.digital.