Restarting iPad when iPad won't turn off

Are you sure that you performed the forced restart properly? You do not have to turn the device off in order to do the forced restart. Typically a forced restart will get you out of the frozen screen scenario.

You can try the other steps in here. You will need to use a computer for the third suggestion.

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

You don’t turn it off to do a forced restart. Depending in which iPad you have use the appropriate method. Your tag line shows that you have an iPad Pro, but just in case both ways are listed below.

• iPad models with Face ID: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Power button until the device restarts.
• iPad with Home button, iPhone 6s or earlier, and iPod touch (6th generation) or earlier: Press and hold both the Home and the Top (or Side) buttons until you see the Apple logo.