Help me

You are correct that you should and will only see the picture that was just taken with the screen locked in the Camera app. If that is not happening then you are probably unlocking your iPhone by raising it to eye level (to view the Lock Screen to open the Camera app). Face ID is unlocking your iPhone before you can activate the Camera app. That is normal operation.

To test this theory, Lock your iPhone and hand it to someone else to activate the Camera app. You will notice that the other person will not be able to see the rest of the pictures on your iPhone as long as the iPhone is still screen locked.

Axel F.

There are no steps to follow other than ENSURING that the iPHONE is LOCKED as the Camera app is activated.

 Try and Force Restart your iPhone EXACTLY as shown below and see whether that resolves the issue:

• Press and quickly release Volume UP button
• Press and quickly release Volume DOWN button
• Press and Hold the SIDE button until an Apple logo appears and then release the Side button (Can take up to 20 seconds. (DO NOT release Side Button when invited to Slide Power OFF). 

Axel F.

You are welcome.

Axel F.

Do you have Face ID and a passcode setup to unlock your phone?

I just tested on an iPad with the passcode removed and it behaves in the way you are describing