Hi, we'd request you follow the below steps:
1. Clear cache & storage of Camera App after backing up & disable/re-enable camera App
2. 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
# How to enter and exit "Safe Mode"
https://www.asus.com/support/FAQ/1005163/3. If still you face the issue factory reset your phone after taking a full backup:
https://www.asus.com/support/FAQ/1006346/4. Last option would be to visit the service centre to have
a check. Locate here:
https://www.asus.com/in/support/Service-Center/India
