If you want to turn off the camera on your iPhone or iPad - remove it from the lock screen and also hide the Camera app - you need to take a quick trip to Screen Time in Settings. See how you can make the necessary adjustments.
The secret is "Screen Time"
Each iPhone or iPad includes a special feature called Screen Time that can be used either to monitor and restrict the use of your application or as settings. parental control for children who may be using the appliance. In our case, we will use Screen Time to restrict access to the Camera app, which will also remove the camera app shortcut from the lock screen on iPhone and iPad.
While Screen Time can be used to disable other applications, by default, it only restricts what you select, so using it will not affect the classic functions of your iPhone or iPad.
How to disable the camera app
To disable the application Camera on your iPhone or iPad, you must use Settings. First, launch the Settings app on your iPhone or iPad.
In Settings, press "Screen Time".
If you have already enabled Screen Time, go to the next step. If you have not enabled it, press "Turn on Screen Time" and then press "Continue" and select "This is My iPhone" or "This is My Child's iPhone" based on your personal preferences. Any option will work to turn off the camera.
In the Screen Time settings, scroll down and click "Content & Privacy Restrictions".
In the "Content & Privacy Restrictions" section, click "Allowed Apps".
In the "Allowed Apps" section, turn the switch next to "Camera" to turn it off.
After that, you are done.
If you want to set a password to prevent someone from activating the camera, double-tap until you go back to the Screen Time settings main page. Click "Use Screen Time Passcode" and then follow the instructions to set one.
Also, if you need to turn Camera on again later, go back to Settings> Screen Time> Content & Privacy Restrictions> Allowed Apps and turn the switch next to "Camera" to "On". You can also turn off Screen Time completely in Settings> Screen Time by selecting "Turn off Screen Time".
Source of information: howtogeek.com