Stuck or dead display pixels are unusual - but not unknown. There is an industry-wide scoring formula that is used to determine whether or not one or more pixels are considered to be a warranty defect.
Should you have benefit of an active AppleCare+ plan, regardless of warranty you may be able to make a claim.
You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:
https://apps.apple.com/gb/app/apple-support/id1130498044
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assess your iPad:
Genius Bar Reservation and Apple Support Options - Apple