Maybe you can help me on that part.

These ESP32 devices and the Android apps are standalone servers. Can host the apps and data from users independently.

The central geogram is useful as canonical source of truth for devices to discover other devices but I'm not at all too happy because one single DDoS would be enough to bring it down.

For now it is working that way centralized but we should come up with a more resilient way for peers to synch data between each others without the geogram central being necessary.