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

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.

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.