Screenshot Not Working on iPad

For the 6th generation iPad, you need to use the power button and the home button.

First, here is the documentation that describes how to trigger the screenshot:

Take a screenshot on your iPad – Apple Support

Assuming that your iPad has a Home button - to trigger a screenshot, you simultaneously press both the “top” (Sleep/Wake) button and the Home Button. For iPad devices without a Home Button, the process is the same - but instead uses the “up” Volume button. If the timing isn’t right, something other than a screenshot is acheived.

So, to break this down to reliable sequence that consistently works...

1) Press-and-hold the Top Button

2) Press-and-release the Home Button | Up Volume Button

3) Release the Top Button

Now, press the buttons in the stated sequence - quickly; the screenshot is triggered at (2). After a little practice, the sequence becomes second-nature - and you will trigger a reliable screenshot every time.

If you have an Apple Pencil, a further option exists. Using the Pencil, from the bottom-left or bottom-right corner of the screen, swipe toward the centre of the screen; this triggers a screenshot.

I hope this insight and clarification proves to be helpful.