How to Fix the iOS 11 Camera Not Working
1. Close the Camera App completely.
If you find problems with the iOS 11 camera app during usage, close the app from the App Switcher and then open it again.
For most iPhone models that have a Home button, to completely close the camera app, double tap the Home button to bring out the App Switcher, and then swipe the Camera app up to close it completely.
For iPhone X users, swipe up from the bottom of the screen and pause in the center of the screen to open the App Switcher, and the press and hold the Camera app until there's a Close button on the app, then you can tap on the button or swipe up to completely shut down the camera.
2. Restart your iPhone.
Sometimes small issues like app crashes could be fixed by simply rebooting your iPhone. It's a common solution for a lot of bugs and errors on iPhone and a lot of other electronic products. So when you find an iOS 11 camera bug, instead of getting frustrated, try restarting your iPhone first and see if it gets back to normal.
Press and hold the Power button on your iPhone until the Slide to Power Off bar appear. Slide to turn off your iPhone and then press the Power button again after it's been completely shut down to turn it back on.
To turn off iPhone X, press and hold the Side button and one of the Volume buttons at the same time. And then the Slide to Power Off bar would appear.
3. Reset iPhone Settings
If restarting your iPhone doesn't work, try resetting all the settings on your iPhone. It will only reset the system settings and won't damage your person data like photos and messages.
Go to Settings>General>Reset and tap on Reset All Settings.
4. Check for new iOS Updates
Usually if there's a bug in the old version, Apple would have the bug fixed in the latest update. So check and see if there's any update available and update immediately when you can.
Go to Settings>General>Software Update to check for the latest update.
5. Check if you have run out of storage space
One possible reason why you can't take a picture with your camera is that you may have used up your storage space and there's none left for more photos. Go check and see if that's the reason.
Go to Settings>About>Available and see how much space is left on your iPhone.
For more details, check: iOS 11 Camera Not Working:How to Fix