I go on my browser (Google) or whatever you might use. I type in Ytmusic converter and copy the YouTube link into it. You can turn it into an Mp3 file and download it to your phone audio section. Then, next time you go into ringotones and want to pick a song, you should be able to search it in your phones downloaded audio.
To set a song from your YouTube Music Playlist as your ringtone, you can use a third-party converter like YouTube to mp3 to download the song as an mp3 file. Once downloaded, you can then use your phone's settings or a ringtone maker app to select the mp3 file and set it as your ringtone. Make sure to respect copyright laws and only download content for which you have the necessary rights.
