I use the nextcloud gpodder integration myself with antennapod (phone) + kasts (desktop) and it mostly works well with subscription sync and timestamp sync. It’ll occasionally forget that I’ve listened to an episode on desktop but I guess that’s just growing pains.
I’ve been keeping an eye on podfetch as a potential nextcloud-gpodder replacement but it’s not just there yet for me.
As for finding an alternative to the sync server, my only suggestion is to find a free/paid option at github.com/nextcloud/providers#providers that’ll let you install the gpodder nextcloud app or use the oracle free tier to host something light like podfetch.