YouTube needs to update. I suspect they will soon. A ton of people upload vids from iPhones.
Another temp solution aid to download YouTube vid using 4K Video Downloader and then use a media player like VLC.
Both are free to use software.
Josh
2020-12-03 21:19:37 +0000 UTC
If you see oversaturated or over-vivid colors in the video playback, the basic issue is that online media platforms aren't caught up with codec support for the iPhone12 yet - there are several discussion threads at Apple.com. The only "fix" I've seen this morning is Apple is recommending turning off Automatic HDR (results seem mixed). My workaround was to watch the video through a smart TV device (I think I have a Roku3 set up in that room), and that seemed to work okay.