[armincerf]

"syncing doesn’t work without a server"

I don't think this is true, granted there are some big challenges to transfering data between devices without a central server, but there are several projects like https://dxos.org/ which use p2p, and also there's https://ditto.live/ which uses bluetooth/wifi direct for cases where all users will be in the same room or on the same local network (imagine wanting to play chess with a friend sitting in a different row on a plane without wifi - I was in this situation recently and was pretty surprised that I couldn't find anything on the app store that could do this!)

Of course most of the time its better to have a server because p2p still has a lot of difficulties and often having a central 'source of truth' is worth the costs that come with a server based architecture. So imo things like https://electric-sql.com/ or https://www.triplit.dev/ or the upcoming https://zerosync.dev/ will be far better choices for anyone wanting to build a local first app used by many users.