It also polls, it just does it as part of the OS. Power saving by the OS can often interfere with apps like nfty that want a long-running background process, especially if they haven’t been opened in a while.
From what you're saying, it doesn't sound like the OS-based polling would be more power efficient, as someone in this chain suggested, just more reliable. Though, I think you can just turn off battery optimization for the ntfy app, in which case I'd expect them to be on par.
If that's right, it seems like ntfy with battery optimization turned off is effectively a "real" push notification system.
