Screenshots are not triggered using the Accessibility Assistive Touch feature - but can be triggered using the iPad's physical buttons, or more easily using a corner-swipe gesture.
Screenshot using iPad physical buttons:
Take a screenshot on your iPad - Apple Support
Screenshot using corner-swipe gesture:
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
iPadOS 17
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