How do I stop my iPhone 13 from using 4G data when idle?

You may --> Check the cellular data usage on your iPhone and iPad ...

Worried about data consumption?

1. Disable Push notifications for apps you do not use often --> Use notifications on your iPhone, iPad, and iPod touch - Apple ...
2. Location services to be allowed only while using the app --> Turn Location Services and GPS on or off on your iPhone, iPad
3. Set your iPhone to fetch email and calendar data from internet less frequently --> Push Fetch email Settings - Apple Community
4. Turning off Background App Refresh --> Switch apps on your iPhone, iPad, or iPod touch - Apple Support
5. Disable auto backup for any third party apps (e.g. WhatsApp) --How to back up to iCloud - WhatsApp FAQ
6. Uneasy about automatic App updates? Turn on or turn off automatic updates. 
7. Disable WiFi Assist --> About Wi-Fi Assist - Apple Support

Go to Settings > Cellular, then turn Cellular Data on or off for any app (such as Maps) or service (such as Wi-Fi Assist) that can use cellular data. If a ...

View or change cellular data settings on iPhone

When Exchange ActiveSync is enabled on an iPhone, it uses continuous background data to keep your email, contacts, calendar, and other synced items up to date in real-time. This ongoing synchronization can contribute to increased cellular or Wi-Fi data usage and may also impact battery life, especially if push updates are frequent.

1. Is this your corporate/organisation/enterprise/School Management iPhone? Then please contact the system administrator of your corporate//organisation/enterprise/School Management
2. If it is your device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

A corporate profile installed on your iPhone could potentially be contributing to the inaccessibility of certain features. 

Here's why:

• Restrictions: Corporate profiles can have restrictions placed on apps and functionalities. These restrictions might be limiting some activity, causing it to be unresponsive or quit.
• Managed Apps: IT departments might deploy specific navigation apps through the profile, potentially blocking certain functions or features.
• Security Settings: Corporate profiles often have stricter security settings that could affect app or function behavior. This might be causing unexpected behavior of an App or functions.

Here's what you can do:

• Check with IT: The best course of action is to contact your IT department. They can explain the restrictions set by the corporate profile and see what is affected. They might be able to adjust settings or suggest alternative apps or features approved for corporate use.
• Look for App Conflicts: See if your IT department uses a different app through the corporate profile. Conflicting apps might cause crashes.

Additional points to consider:

• Even if the profile isn't directly affecting the function, it's still a good idea to check with IT. They might be aware of similar issues and have workarounds.
• While troubleshooting, make sure you prioritize safety. Don't fiddle with your phone. 

By working with IT and considering these possibilities, you can hopefully identify if the corporate profile is the culprit and find a solution that allows you to use the iPhone to your liking.

Try this --> Push and Fetch options on email account o… - Apple Community