Why does the LCD display have a Yin and Yang screen?

This is caused by the uneven brightness and color temperature of the display, which seems to be the cause of the backlight technology. Not only low-end monitors, even Dell's up2718q, there is this situation. Although some high-end displays have a uniformity compensation function, the contrast will be lost after turning it on, so it is better not to turn it on. If you want to pursue uniform color temperature and brightness, you can only choose EIZO's CG series, but if your eyes are sensitive enough to color, you may be able to see deviations.