iPhone 16 Plus on iOS 18.6.1 lags in Settings > Mobile Service even after reset

On a user-to-user site, we are unable to remotely connect to your iPhone to run diagnostics, and without having the phone in our hands to test, we have nothing to go on.

Have you run Diagnostics on the phone yourself? Have you taken the phone in to have service check it out?

How to put your iPhone in diagnostics mode - Apple Support

If this were a bug with iOS 18.6.1, this site would be flooded with posts about the same topic. It's not.

There may be several reasons why a device may behave as described by you, and none of them are related to iOS 18.6.1.

Let's delve a bit deeper into some of them:

1. iPhone Storage: A full iPhone can slow things down. Phones can experience performance issues when the storage is nearly full. Users can check their storage status by going to Settings > General > [Device] Storage. Deleting unnecessary apps, photos, or videos can free up space and improve performance. How to check the storage on your iPhone and iPad - Apple Support.
2. Device's Battery Health: A degraded battery can impact performance. A deteriorating battery can impact the overall performance of an iPhone. Checking the battery health can be done by going to Settings > Battery > Battery Health. If the maximum capacity is significantly reduced, it might be time to replace the battery. Prolong and Maximise Battery Performance … - Apple Community
3. Incorrect Handling of the device: Accidental drops or bumps can cause internal damage. Looking at Apple's guide on proper handling is a good step. Important handling information for iPhone - Apple Support (IN)
4. Environmental Issues: Extreme temperatures, dust, and water exposure can all be detrimental.
5. Keeping the iPhone/Watch and Airpod clean is an important step. Dust accumulation in the device's ports and openings can affect functionality. Apple provides guidelines on how to clean iPhones safely, which usually involves using a soft, lint-free cloth to remove dust without causing damage.
   1. 1. Cleaning your iPhone - Apple Support
      2. How to clean your Apple Watch - Apple Support (IN)
6. Clean your AirPods Max - Apple Support
7. Keep the iPhone within temperature limits. Phones are designed to operate within a specific temperature range. Exposure to extreme temperatures, especially in parked cars, can lead to overheating or other performance issues. If your iPhone or iPad gets too hot or too cold - Apple Support.
8. Addressing safety issues is also important: Important safety information for iPhone - Apple Support (IN)
9. Unauthorized Service: Servicing a device through unauthorized channels can result in substandard repairs and void warranties. Users should always seek authorized Apple service centers for repairs and maintenance.
   1. Repairs by unqualified technicians can introduce new problems. Find information about your warranty or AppleCare plan - Apple Support is helpful.
   2. Modification / Alteration of a device by a third-party vendor may cause issues beyond repair. --> Unauthorized modification of iOS - Apple Support (IN)
10. Jailbreak on iPhone: Now, let's talk about jailbreaking. Jailbreaking removes Apple's restrictions, allowing for more customization and app installation outside the App Store. However, it can also lead to instability, security vulnerabilities, and issues receiving future iOS updates.

By considering all these possibilities, you've provided a comprehensive approach to troubleshooting the iPhone's behavior.

Understanding and addressing these factors can help you maintain their iPhones' optimal performance and longevity. Following Apple's guidelines and seeking authorized support when needed are crucial for a positive user experience.

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...