Ask HN: FOSS Firebase/Supabase alternatives to try?

I'm building a project in Supabase right now and I'm strongly considering switching.

One big issue I ran into is they suggest using hCaptcha to prevent abuse of anonymous user sign ups. The problem here is there isn't really a clear way to integrate this with a game engine, for example if I want to develop a unity client for my game later, I'd have to open up a web view inside of unity or something. Ideally I would just like to enable hCaptcha when registering new users, but there's no way to configure this with Supabase.

Firebase apparently doesn't care, and while it's great, it's closed source which doesn't make too much sense for an open source game.

I need a FOSS solution if possible.