Unable to screen shot after latest iPad update

By far the easiest method to trigger and save a screenshot is to set-up and use the corner-swipe gesture.

iPadOS 17/18

Settings > Multitasking & Gestures >

• Swipe Finger from Corner - set to ON
• Bottom Left Corner > select Screenshot or Quick Note as required
• Bottom Right Corner > select Screenshot or Quick Note as required

iPadOS 16 and earlier

Settings > General > Gestures > 

• Allow Finger Swipe From Corner - set to ON
• Left Corner Swipe > select Screenshot or Quick Note as required
• Right Corner Swipe > select Screenshot or Quick Note as required

Now that you have enabled the corner swipe, you can easily capture a screenshot with just your finger. Just swipe diagonally from the lower-left or lower-right corner of the screen towards the centre; this will immediately trigger the screenshot.

You can also trigger a screenshot using an Apple Pencil:

Settings > Apple Pencil > [Pencil Gestures] Left | Right Corner Swipe - select Screenshot for one, other or both gestures

The other ways to trigger a screenshot from an iPad are described here:

Take a screenshot on your iPad - Apple Support

If a restart dit not work you might want to give this as feedback to apple to let them look into the issue

Product Feedback - Apple

You're very welcome. I'm delighted that the outlined solutions proved to be helpful to you.