My ipad pro 12.9 appear a white spot on the screen

Can you take a photograph/screenshot - and show us what you can see? If a screenshot will capture the “spot”, then the artifact is likely to be software related - if it only visible in a photograph, then it is almost certainly a physical screen defect.

It is very difficult to see much in the photo - however, as you’ve attached a photo to illustrate the point, I must assume that you’re seeing a diffuse brighter patch in one or more areas of the screen - resulting in some loss of uniformity backlight illumination across the entire screen area.

Unfortunately, this doesn’t appear to be a particularly uncommon occurrence in “laminated” screens used with some of the higher-end models of iPad - in particular the iPad Pro models. The issue seems, in most cases, to appear over an extended period of time - perhaps suggesting some degradation in the screen construction from use. Equally unfortunately, there’s nothing that can be done to resolve a defect of this type short of screen replacement.

It is obviously disappointing to see this occurring on high-end devices, upon which we have spent so much money. If you are still within warranty (or have extended cover through Applecare) - and you are prepared to argue a “defect” at your local Apple Store - you could seek reparation through this route. If successful, you might be offered an “exchange” with a reconditioned (i.e., “brown box”) iPad of the same model.

If outside of warranty, you might also be offered an exchange for a reconditioned iPad - at a substantial cost. The replacement cost will be somewhat less than a new iPad, but you might personally consider that money being better spent against a new iPad. You might also wish to consider that a reconditioned replacement is not “new” and might come with its own set of problems.

I hope this has been in some way helpful.