I am interested in all things UHD / 4K / HDR, so this caught my attention. Previously, the iOS app from YouTube did not support High Dynamic Range (HDR) video on the three OLED iPhones from Apple. That means HDR10 and Dolby Vision. Well now, so here is a link to more details. Note that Apple's new LCD iPhone, the iPhone XR, also supports HDR video playback, according to Apple's specifications.
: YouTube app for iOS gets HDR support