Congratulations -- I just searched for what is the best YouTube down loader and your post keeps popping up, now I'm stuck in an endless loop. If the answer to every question is "Google it" there would be no point in having this forum or any other forum, The internet would be a very boring place
NewPipe is the new youtube alternative better than youtube venced which you need google services active on Newpipe you don't need it to be able to use it and you can download mp3 from the video Cheers
For me the best one is Dentex Youtube Downloader (apkmirror .com/apk/samuele-rini/youtube-downloader/youtube-downloader-7-1-1-release), it can grab all the video and audio streams and merge them, it's easy to use and not intrusive