How to fix an iPhone X that’s suddenly slowing down, keeps freezing and lagging

If the issue is related to system settings issues or erroneous system configurations, resetting the iPhone's system settings may be a viable remedy. This is usually what happens after applying an update that is intended to automatically override system settings in the event of a conflict. To clear this up, follow these steps to return all of your settings to their original or default values:

1. From the Home screen, select Settings.
2. Select General.
3. A reset can be found by scrolling down and tapping it.
4. Select Reset all of the settings to the defaults.
5. To continue, enter your device passcode if requested.
6. Then press to confirm that the settings have been reset.