According to a tweet by Ishan Agarwal, it appears that in the macOS update, Apple will finally be updating Safari to support 4K Netflix streams. Prior to this, Mac users would only be able to stream Netflix at 1080p, so if you own a Mac like the iMac with its 5K display, then you will finally be able to take advantage of the higher resolution.
What’s interesting is that while Apple did update its Mac lineup to support the HEVC codec that would be required to allow 4K streams, they did not update Safari to take advantage of it, at least until now with the Big Sur macOS update. This is good news for Mac users, but at the same time, there is a bit of a catch.
https://twitter.com/ishanagarwal24/status/1277189882771734528?
According to Apple, Macs that want to enjoy 4K HDR streams will need to be of the 2018 models or later, which means that even if your Mac is macOS Big Sur compatible but it is older than 2018, then you will not be able to enjoy these changes.