My first thought was YT-DLP, but they don’t seem to support Spotify. Spotify-dlp claims it can do this, but I’ve never tried it. Be careful, maybe run it in a sandbox first.

Alternatively you can go the old-school route with Soulseek. It’s a classic peer-to-peer client for sharing files. Lots of music there, but it being peer-to-peer means you will only find files that are being shared right at that moment. So your search results can look completely different every day. Also, Soulseek automatically shares the folder it saves your files to. So make sure you point it at an empty folder for your downloads.