so the way these work usually is 2 piece like old IRC away daemons. You have a headless instance that syncs what you care about on "someone elses computer" or just online all the time. That does the job of keeping up-to-date. Your phone and other devices do a secure connection to that device to get updates. what's interesting about building it to just be the same kind of server is you can simplify deployment and apps (its all the rage anyway just look at a react app).

so your device does not need to be online, you could run things like bots and have schedules and get just the deltas when you come online. This is also how private signing works today so the design and deploy pattern is well documented.