I became quite frustrated with how slowly Spotify tends to load on Android, especially when it comes to podcasts. On Windows and Linux, I've been using Kasts, and added AntennaPod to the mix, but they don't have native interoperable sync. I don't have a full NextCloud instance, but I do have a server for my website, so I wrote a quick patch and systemd service/nginx config to allow both to work.
Note: the passwords written to g2g.db are stored in plaintext (haven't fixed it myself yet), so when you're creating a user, make sure to use a unique and long password.