Hi, friend. To extract audio from video, I personally use online audio extractor - Clideo or an easy-to-use desktop editor - Joyoshare Media Cutter. Both of them can extract audio from YouTube videos without quality loss. More, the latter can convert the extracted audio to any other format and gives editing tools.
There are some YouTube to MP3 converters you can use.
Take a look at https://youtube-dl.org With this, you can download YouTube videos as (typically) MP4 or MKV files and then extract the audio from this. AFAIK can also run youtube-dl with a flag to just capture the audio portion.
Go to YouTube and copy the video link, open the 4K Video Downloader window, and click "Paste Link". The parsing process should take up to several seconds, depending on the video length. Another smaller window will pop up. Select the "Extract Audio" option.