talking totally out of my ass, but apple seems to have robust infrastructure for e2ee communication between your devices, for example it is known that location information in find my is not visible to apple. I’d be surprised if the channel to send iphone notifications to your mac wasn’t also e2ee

Unless something has changed since I last did this, the app's server initiating the apns doesn't encrypt using some public key for the destination. So no e2ee at that layer. But you could encrypt the payload and have the app decrypt it if you're managing the keys yourself.