One suggestion online is to press the sequence of buttons shown in the article below:
https://mashable.com/2015/11/20/apple-ipad-pro-screen-black/#coWqk0nqv8qB
Quoting:
"Learn what to do if your iPad Pro doesn't respond when you press buttons or tap on the screen, and the screen is black," Apple's message reads. "To get back to using your iPad Pro, force restart it by pressing and holding both the Sleep/Wake and Home buttons for at least ten seconds, until you see the Apple logo."
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