"If you look at an OLED display off-angle, you might notice slight shifts in color and hue. At reduced display brightness levels against black backgrounds, you might notice a slight blur or color change while scrolling. These are characteristics of OLED and are normal behavior. With extended long-term use, OLED displays can also show slight visual changes. This is also expected behavior and can include “image persistence” or “burn-in,” where the display shows a faint remnant of an image even after a new image appears on the screen. This can occur in more extreme cases such as when the same high contrast image is continuously displayed for prolonged periods of time.

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We’ve engineered the Super Retina and Super Retina XDR displays to be the best in the industry in reducing the effects of OLED “burn-in.” This includes special algorithms that monitor the usage of individual pixels to produce display calibration data. Your iPhone uses that data to automatically adjust the brightness levels for each pixel as needed to reduce visual effects from “burn-in” and to maintain a consistent viewing experience.

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In addition, all displays, including OLEDs and LCDs, might be susceptible to reduced brightness levels as the display ages over time. This can occur on any consumer-electronics product."

source: https://discussions.apple.com/thread/254041139

Yes you simply “hard format” your new iPhone to the newest firmware available