The iPhone 13 lineup officially went on sale on Friday September 24. As pre-order arrive to their customers' doorsteps or Apple Stores in most markets, folks have noticed that the ProMotion feature isn't working consistently. The iPhone 13 Pro and 13 Pro Max both feature Apple's ProMotion displays, meaning they support refresh rates of 120Hz. The feature has been on the iPad Pro since 2017, but this is the first time Apple brings the feature to the iPhone. iOS 15 supports ProMotion across all apps while scrolling or performing full-screen transitions like switching apps or...
Source: https://www.gsmarena.com/apple_iphone_13_pro_and_pro_max_arent_rendering_all_apps_in_120hz-news-51125.php
