Not that I imagine most people would change it, but notably ntfy means that notifications don't have to go through centralized services. (As you can set what ntfy URL you want to use, including to your own server)

I guess if you set up an `ntfy` server, and you also run the `ntfy` app on iOS, then the `ntfy` app can do a local notification on the iOS device (without going through Apple APN servers)?

Then it looks like you can probably just do the communication between server and app using HTTP(S), though the app either needs to keep a connection open or poll frequently (with entirely new TCP and possibly TLS connection negotiation each poll time):

https://docs.ntfy.sh/config/

https://docs.ntfy.sh/publish/

`ntfy` is impressive, but there's a lot of implementation to it that could have vulns, there's substantial server config to do, the app-side UX polish isn't great, and the connection method is inefficient. But it might not obviously leak to some centralized thing outside your control (unlike if you do iOS push notifications the normal way).