One of the biggest additions to Google's new Pixel 4 line is the new 90Hz refresh rate screen. This is a key trend in 2019 flagship phones but now it seems that both Pixel 4 and 4 XL automatically switch to 60Hz when their brightness is set to lower than 75%. The discovery was made by a group of Reddit users and has since been confirmed by many early adopters. Apparently, there is a workaround to this issue through the developer setting where you can lock the 90Hz refresh rate in all scenarios. In addition, Twitter user Jeff Springer noticed that the 90Hz mode stays locked at lower...
Source: https://www.gsmarena.com/pixel_4s_screen_throttles_down_to_60hz_when_brightness_is_set_below_75_-news-39773.php