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.

Hmm yes maybe. I do remember a paywall bypass extension was removed from there because publishers were complaining to Vercel. Worst case scenario I guess your website gets taken down

You can create a simple static website and deploy it to Vercel for free. You can buy a domain name and attach it pretty easily, but it’s not needed (by default website will have .vercel.app domain).