Yes, this is an FCM replacement on Android (and it can easily fall back to FCM if the user doesn't have UnifiedPush). There is no native UnifiedPush on iOS because Apple doesn't allow background services. The server side to support both is simple, but on the client you would need code for both FCM (for iOS) and UP (for Android). It would be interesting to build an FCM wrapper for iOS into the UP Flutter library.
I don't know too much about this, but is this not APNs [0]? I see there is a FCM integration (which is how I assume FCM does it anyway) [1] as well as a standalone Flutter implementation [2].
How would iOS native only apps on Swift do push notifications, surely Apple has their own service and everyone doesn't use Firebase?
