Taking from Excessive general system services data - Apple Community
Here's the potential answer:
Go to Settings >> General >> Background App Refresh
Then click on "Background App Refresh" and select "Wi-Fi". I had "Wi-Fi & Cellular Data" before.
iPhone 15 Pro Max, iOS 18
You probably have some corrupt data on your iPhone. So the very first thing you should do is a Forced Restart, as the procedure is shown below. Be sure to perform it quickly and ignore the slider that appears midway.
If that doesn’t help, the next thing to do is to backup your iPhone, then erase and restore it from that backup. The support article below explains how to perform it.
Restore your iPhone, iPad or iPod touch from a backup – Apple Support (AU)
I'm still having issues... I use an app to track in details what "General" label is doing and so far I'm still seeing http://updates.cdn-apple.com consuming lots of my mobile data allowance.
I've been dealing with this issue since Dec 24. I've spoken with Apple for 3 times now and I'm still seeing this problem.
Excessive general system services data (Again)!
