If you have set up iOS 14, there is a new feature that enables you to take a screenshot simply by tapping on the back of the device called Back Tap. If you’re interested in this, please read on to set this up. 

What is Back Tap?

• Back tap uses the accelerometer to detect if you have tapped on the back side of your device. 

• within Settings you can set up “2 tap” or “3 tap” to launch certain functions for your device. 

• Do note that whilst Apple classifies it as an “Accessibility” feature, it can be useful for everyone.

How to take a screenshot on iOS 14 by Tapping

• Usually when you want to take a screenshot on your iPhone, you would have to hold down certain buttons at the same time.

• it’s often quite easy to get the buttons mixed up, as you might accidentally lock your device or adjust the volume.

• by enabling the Tap, you can take a screenshot by tapping the back of your device, without needing to do the button prompts.

Setting up Back Tap

• Open settings > tap on Accessibility > select “Touch”

• within Touch, scroll down until you see the “Back Tap”.

• depending on your preference select “Double tap” or “Triple tap”. 

• you will see quite a few options you can set the Back Tap to. To take screenshots using Back tap, select “Screenshot”. 

Now when you next tap on the back of your device 2 or 3 times, this will take a screenshot for you.

Source & Further Reading: 

https://www.howtogeek.com/690823/how-to-take-a-screenshot-by-tapping-the-back-of-your-iphone/