I would rather prefer that you would buy spotify premium if you can. But, till you can, there’s always spotdl which can allow you to download your songs
Installation of spotdl (github page click here): https://i.imgur.com/5g6uUgD.png
https://paste.debian.net/plain/1293528 a very simple script, you don’t actually need the script, but it makes it easier to download songs.
btw, I am using file manager nemo here, if you want something else, change it to your default file manager, if you don’t want to open folder, well remove last but one line.
execute this command first and when nano text edit appears, paste the debian pastebin in there.
Apparently this script uses Youtube as source for downloads.
I don’t know much about that :(
But spotify playlists won’t convert to youtube playlists thus, I doubt if I can