A certain dark spot appeared in the lower left corner of my iPhone XR, in the form of a rounding of the screen

Last night I noticed that a certain dark spot appeared in the lower left corner of my iPhone XR, in the form of a rounding of the screen, this does not depend on temperature and humidity in the room. On white and black colors it is almost invisible, but on gray it is very visible. Has anyone come across this?

[Re-Titled by Moderator]