On iOS, is there any way to see what the “Documents & Sync” system service is using cellular data for? I’m using iOS 13.2 on an iPhone X, and would like to drastically reduce the amount of cellular data my phone is using. In less than a month, my phone has used 10.7 GB of cellular data. 8.5 GB of that is from “System Services,” with 7.9 GB coming from “Documents &amp; Sync.”

Is there any way to see what is using all of that data, or to control what happens over cellular vs waiting for Wi-Fi? My battery also dies quickly, and assume that is related to how much cellular data is being used in background. 

What I tried: 


I turned off iCloud Drive syncing over cellular network yesterday morning and then reset cellular data usage statistics. Since then, Documents &amp; Sync has used used 1.0 GB of cellular data .
I’ve had “Low Data Mode” turned on under Cellular Data Options for the entire month, which doesn’t seem to be helping at all.
I tried erasing all content and settings and restoring from backup. This may have helped slightly, but it still seems to be using large amounts of cellular data
Take a look at "Wi-Fi Assist", which is found at Settings --> Cellular --> right near the bottom of the list.  This setting uses your cellular data when Wi-Fi connectivity is poor.  

This may account for cell usage even when you have iCloud Drive turned off.