so before (few months ago) there was possible in DuckDuckgo search engine to search YouTube/Spotify song, or few of choice containing public playlist with:
site:youtube.com inurl:"playlist" " " "song name" Orsite:spotify.com inurl:"playlist" " " "song name" (it may be/been different for Spotify check refereed link below)
It does not work anymore it's ether duckduckgo sold off (in google this method was not working), or YouTube changed algorithm.
Could you provide differential working method?referring to:How to search Spotify playlists by song?