Part of that is the responsibility of the app developer, since they define the payload that appears in the APNs push message. It’s possible for them to design it such that the push message really just says “time to ping your app server because something changed”. That minimizes the amount of data exposed to Apple, and therefore to law enforcement.

For instance the MDM protocol uses APNS. It tells the device that it’s time to reach out to the MDM server for new commands. The body of the message does not contain the commands.

That still necessarily reveals some metadata, like the fact that a message was sent to a device at a particular time. Often metadata is all that law enforcement wants for fishing expeditions. I think we should be pushing back on law enforcement’s use of broad requests (warrants?) for server data. We can and should minimize the data that servers have, but there’s limits. If servers can hold nothing, then we no longer have a functional Internet. Law enforcement shouldn’t feel entitled to all server data.