I've been wondering about this as well, is there an IMDBID equivalent global identifier for songs/albums? I would guess not.
There are a bunch of Spotify -> (YouTube|Tidal|Deezer|...) playlist converters on the internet, but from the FOSS implementations I've seen they rely on searching the title/artist across multiple platforms and grabbing the first result. There isn't anything that can reliably match songs, albums, or artists across platforms.