What’s causing these screen artifacts?

Rendering is often the heaviest of processing jobs your system is asked to preform and creates by far the most heat. While Apples M series SoC runs cooler than Intels CPU, Apple cut back on this series cooling as such you maybe expecting a bit to much from it.

Here we have the signs of the T-CON logic which is that dangling piece attached to the display that sits inside of the upper case. Review this image while not the best the silver shield area is the logic which has either over heated or the ribbon cables/LCD panel has failed. In any case replacement will be needed Display Assembly Compatible with MacBook Air 13" (Late 2018-Early 2020)