Your fifth generation iPad Pro has a mini-LED backlight system.
Unlike the previous design that takes light emitting from the edges of the display - and evenly distributes it across the entire back - the Liquid Retina XDR display uses over 10,000 mini-LEDs spread uniformly across the entire back of the display, delivering higher LED density than any other display of its kind. These mini-LEDs are grouped into an array of over 2,500 individually controlled local dimming zones.
As illustrated in your attached image, the display controller that controls the dimming zones may have a fault - and/or one or more dimming zones may actually have failed - both being a hardware fault that can only be resolved by way of a repair.
You would be best advised to visit the the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) where the technicians will be able to test and assess your iPad - and you can explore your available options:
Genius Bar Reservation and Apple Support Options - Apple