Xiaomi Mi 8 owners report that they are receiving an OTA update containing MIUI 10 9.5.22 that adds the promised DC dimming feature of the screen. It's around 324MB big and so far, it has been rolling out in China so it might take some time before it hits the global version. The changelog only says that it brings DC dimming, fixes the IC of the OLED panel to eliminate the flicker. You will have to go to the Settings menu, tap on Display and toggle the Anti-Flicker function. This is great news for those sensitive to PWM, who will probably feel quite relieved when spending a lot...
Source: https://www.gsmarena.com/xiaomi_mi_8_gets_miui_10_9522_introduces_dc_dimming-news-37171.php