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ornapat wrote:

The centre of the screen is brighter than usual.

Begin with a forced-restart of your iPad - as this will often clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

After the restart, test your iPad screen by viewing a "flat" (i.e blank) white background. Don't rely upon a wallpaper image - as the chosen image/photo may, by its very nature, have variations.

When assessing the screen with a flat-white background, if its brightness is inconsistent or uneven, this might suggest partial delamination of the screen backlight diffuser layer - or failure of one or more of the edge backlighting LEDs. If any element of the screen has failed, the only available remedy is full replacement of the iPad's screen assembly.

You might be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to hands-on test and assess your iPad. If a fault is identified, you'll be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange a qualifying iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair while expensive will be somewhat less than the cost of a replacement iPad.

As for out-of-warranty repair costs, Apple offers a fixed-price price repair. You can verify eligibility and cost for your region/country here:

iPad Repair & Service - Apple Support

If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.