It is always good to save some time when you are on the go and if you would like to take a quick screenshot using your iPhone here is the way to do it.
Go to settings
Select Touch then scroll down to the bottom of the screen and select Back Tap
Select Double Tap
Now every time you want to take a screenshot all you do is double tap on the back of your screen.
You can either edit, markup or just share your screenshot if you like.
You must have at least on iPhone 8 running IOS 14 or later for this to work.