I was wondering how it would work when someone is offline and was sent a message without a server. I personally haven't used this but I have been looking for a replacement for Signal that would be a little more normie friendly that syncs across multiple devices.

I got this from their GitHub

"Asynchronous messaging: because messages sync to all members, members can communicate without being contemporaneously online, provided that there is "continuous liveness", a continuous chain of online peers who each sync the latest updates, between the sender and the recipient."