Most all of the apps sync with iCloud so it syncs across all of my devices.

However the MediaWatch app syncs between me and my wife which iCloud does not support (as a sidenote, this is one of the hallucination traps that both Claude and ChatGPT led me down -- both said it was possible, and after a few weeks and many, many hours, I learned the major constraints. I was not wanting any of my apps on the Appstore, so that blew that option). Anyway, I ended up making a small simple SQLite database using python on my Pi and use that for my sync needs. The devices only sync while at home, which was not a problem for me. Also I'm not exposing the database to external security issues.