OnePlus 8 Pro officially went on sale on April 29, but prior to that, the company was shipping devices to customers who made pre-orders. It was noticed that some pre-order units had problems displaying them, with issues ranging from squashed / clipped blacks and even "green tint". The tech giant reacted quickly and vowed to nominate an OTA that would fix the problem. Apparently the OxygenOS 10.5.5 update was dropped for OnePlus 8 Pro devices and only fixed the green tint issue. 
It seems that OnePlus has confirmed that the problem with displaying the black background is a hardware problem. A Reddit user post indicates that the company provides users with three options. The first is to send the device for repair to a service center. The buyer can also return the device and receive a refund. Finally, they can submit a replacement request online and receive a replacement. 
We could not verify the authenticity of this statement, but if it is true, then this is a long-awaited event. Most buyers are likely to opt for a replacement or refund option that can then be used to purchase a new one. The OnePlus 8 Pro sells for about $ 900, and it's so much to fork out, and then proceed with such a repair of the device.
( source)
