My AppleTV is in standby and still connects to Apple servers. Why and how to switch off?
Why? It's checking for the above-mentioned data.
Standby does not mean 'off' on any device these days. Your smart TV &amp; cable TV box will be doing just the same sort of thing - Updating TV schedules, checking for messages from various services, checking for OS updates, etc etc.
Note: the entirety of 17.x.x.x belongs to Apple. You can really just allow the entire subnet.