https://wccftech.com/youtube-now-supports-hdr-video-playback-on-iphone-11-pro-11-pro-max/

YouTube on Apple's latest iPhone 11 Pro and iPhone 11 Pro Max now supports HDR playback, taking full advantage of Super Retina XDR display.

Available as a free update straight from the App Store, the YouTube app now finally supports the playback of HDR content on the iPhone 11 Pro and iPhone 11 Pro Max. And yes, in case you are wondering, that is not a typo, the iPhone 11 is not included in the list of supported devices in the latest update despite having a wide color gamut.