Hi, we'd request you follow the below steps:
1. Check your phone for latest software version.
2. Clear cache & storage of Camera App after backing up & disable/re-enable camera App
3. Try the same under safe mode:
Hold the power button for 5 seconds => When the screen flashes with option => Press & hold power option => You will get an option to restart in safe mode
4. If still you face the issue factory reset your phone after taking a full backup:
https://www.asus.com/support/FAQ/1006346/5. Last option would be to visit the service centre to have a check. Locate here:
https://www.asus.com/in/support/Service-Center/India