I haven't seen this posted, but I have the most updated version of Youtube on my iPhone X and I watched an HDR video last night, it was labeled as HDR, but it looked pretty normal for a youtube video, but, last night I noticed, wow the colors looked so much better, then I checked the quality settings and I noticed, it's only up to 1080p, but, the Youtube app now lets the iPhone X playback HDR videos in HDR, tested it on numerous and they all looked great one after another. Just thought I'd share that with everyone.