On a mac run little snitch. On a current ios iphone, I'm uncertain but i run an older version of ios with adblockios.
It contacts a whole slew of apple and 3rd party sites. the main one is that it contacts *.ls.apple.com all the time (location services) even with location services turned off. lots of other apple sites. third party is akamai all the time, but also sites like phicdn.net and att.net (I have an at&t iphone). I do not have any at&t app installed.
on macos catalina, you can (currently still) run little snitch and all kinds of services start contacting apple. and new ones have shown up like touristd and rapportd. Every time you try to pull up a help page. Every account you configure, apple based or not. sigh.
I wonder whether the ls.apple.com servers are connected with security features like "Find my iPhone". But then, I'm not sure exactly what Find my iPhone does if it's turned on but location services are disabled.
I see this sort of claim often, but reliable information about the specifics is hard to come by. Can you share any?