iPhone 11 discoloration

I have purchased a black iPhone 11. Within 2-3 months, I started seeing white metallic spots on camera's outer ring and near the charging point. Then I got to know, those spots are due to discoloration. I have always kept a good back cover on the phone, but these spots keep on occurring.

But as per Apple support, this defect is not covered in the warranty.

It is very frustrating to see this kind of defect and bad service from such a big mobile company.

Can someone help, how to stop discoloration defect and to repair them is possible.