I’ve used Exportify (https://github.com/watsonbox/exportify) to get CSVs of my playlists. I do it for kind of disaster recovery scenario, so I’ve never actually had to re-import my playlists. Judging from the readme it seems it’s possible but tedious. And as for importing to a different service, no idea.
It does require you to log in with your Spotify account though. But I think it’s trustworthy enough and also you can self host it.
Taringa, it was the go-to place for everything, especially content in spanish