Screenshots are coming up as black screens since I updated to 11.1.1

Have you tried turning your iPhone off and on again? If that does not help, try forcing it to restart by holding the home and on/off buttons until you see the Apple logo.

That method only works on the older phones. Here are the instructions for all phones -

• On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo.
• On an iPhone 7 or iPhone 7 Plus: Press and hold both the Side and Volume Down buttons for at least 10 seconds, until you see the Apple logo.
• On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons for at least 10 seconds, until you see the Apple logo.