iPhone X and other iPhone users are facing issues that after iPhone updated it to iOS 11.2.x and restored from backup, the search option is not working in setting apps in iPhone. This is bit annoying issue is same backup is working fine with older iPhone that user had and search was working fine. This seems to be a bug in iOS 11 and most of iPhone X users are affected by this issue.
You can't do a search in the Settings app and if you type something in to find a setting, nothing shows up. Even hard and soft restart to the iPhone does not seem to help. Even the same issue reported with Spotify app as in ios 11 spotlight search not working.
How to fix iPhone search not working in iOS11:
Fix 1: change Language Settings for iPhone.
In case you have upgraded your iPhone X from existing backup, you may change payment card, or get new virtual card with 0$ balance a this may be cause for the issue. After try to get payment for iCloud, cache Settings will be erased and Search in Settings and in Spotlight will be work again.
Fix 2: Reset All setting
Please make sure you have latest backup before trying this as this will erase all user data of your iPhone.
Many users solved it by doing “reset all settings” in Settings->General->Reset. However there are chances that search settings for apps installed after the reset, will not work and you may have to reset phone again.
Fix 3: keep updating iOS
It is always recommended to upgrade iOS as Apple might be aware of this issue and possibly releasesa a permanent fix in upcoming releases.