Are you using— or have your used— a stick-on screen cover or "protector?" That looks like the kind of damage they can produce when removed. They should all be "burned with fire."
Display defects in iPads are not user-fixable. If a restart does not change it, then I can only recommend having Apple evaluate, not a local "repair shop."
Were I a betting man, I'd lay money on the iPad having experienced some form of point-pressure damage and the pixels in the area affected are failing progressively.
Odd that the defect shows a distinct pattern. The only internal component under the screen at the point appears to be the approx center of the battery. Have you noticed any power-related issues? Short runtimes between charging? Sudden shutdowns or screen flickering when the battery seems to have plenty of charge?
A leaking or otherwise damaged battery requires immediate attention. From Apple.
Apple's repair estimate for "other damage" shows a US$419 replacement cost for a wifi-only iPad Air 5. Add US$50 for the wifi+cellular model.
iPad Repair and Service - Apple Support