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You make no mention of your iPad model.
The issue that you describe/illustrate is a most commonly attributed to a physical screen defect known as “stage-lighting” - where some of the backlight LEDs have failed. This is a hardware failure, unrelated to your recent software update.
The screen backlight is illuminated by a row of LEDs positioned along the edges of the iPad screen; a screen diffuser nominally distributes the light evenly across the visible screen. When some of the LEDs fail, you see dark patches - as illustrated in your photo.
The only remedy is replacement of your iPad screen. Unless your iPad is within warranty, or you have an active AppleCare+ plan (that provides cover for screen defects/failure), the cost of repair is unlikely to be economic.
iPad Repair - Official Apple Support
You might be well advised to visit 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: