Until now, Apple users can&t watch videos in 4K resolution on the iPhone or iPad, nor on a Mac Pro or iMac on YozuTube - this will change with the next version of the operating system.
Apple&s new macOS 11 BigSur will be the first to support Google&s open VP9 codec, which YouTube has been using for about three years to play video in higher resolutions. Until now, Apple users had to go through a other browser such as Google&s Chrome or Mozilla&s Firefox, which support VP9, in order to view YouTube video in 4K (and higher) resolution.
According to Realease Notes of the latest macOS 11 Big Sur Beta Apple will support 4K HDR videos via OS, with the advantage that the decoding will be done by hardware and thus the processor will be much less stressed. Beta testers also report that 8K video playback on a MacBook Pro will be smooth.
Also the VP9 codec will be supported by the upcoming tvOS 14, Apple&s TV 4K, which was previously limited to the playback of 1080p YouTube videos. And iPhones and iPads will also be able to display higher resolution videos via VP9 with the next version of iOS 14 - beta testers have already discovered the option for 2160p playback in the YouTube app.
The question is, when Apple will also implement the more and more widely used AV1 video codec, the successor of the VP9 codec - after all Apple is a member of Alliance for Open Media (AOM), which develops the AV1 codec.