What's curious about this behavior, though, is a lower screen brightness puts less drain on the battery, and could potentially offset some of the battery life loss that might occur from running at 90Hz. But the way this is implemented, it might actually discourage users from lowering the Pixel 4's screen brightness. Nevertheless, it's all part of Google's Smooth Display technology.
"We designed Smooth Display so that users could enjoy the benefits of 90Hz for improved UI interactions and content consumption, while also preserving battery when higher refresh rates are not critical by lowering back down to 60Hz," Google told The Verge.
"In some conditions or situations, however, we set the refresh rate to 60Hz. Some of these situations include: when the user turns on battery saver, certain content such as video (as it’s largely shot at 24 or 30fps), and even various brightness or ambient conditions. We constantly assess whether these parameters lead to the best overall user experience. We have previously planned updates that we’ll roll out in the coming weeks that include enabling 90Hz in more brightness conditions," Google added.
In the meantime, there are workarounds available. One is to root the Pixel 4 and change the "config_brightnessThresholdsOfPeakRefreshRate" in arrays.xml from "74" to a different value. However, there's an easier way that does require root access.
If you own a Pixel 4 or Pixel 4 XL and want to prevent it from ever dropping down to 60Hz, go into Settings > About phone and tap the build number five times. This is not voodoo magic—it enables access to a hidden menu called Developer options.
After you enable the menu, navigate to Settings > System > Developer options > Force 90Hz refresh rate and flip the toggle. Just keep in mind that the phone will now always run at 90Hz, even in other situations where a lower refresh rate might be the better option, such as reading a PDF document or ebook (you can still change it manually, though).