Filipe Espósito, 9to5Mac:

Netflix has been offering 4K content for a long time, but Mac users have never been able to watch them due to hardware limitations, since the platform relies on the HEVC codec.

And:

With macOS Big Sur, which is currently available as a beta developer, Mac users can finally watch movies and TV shows on Netflix in 4K resolution. It also works with Dolby Vision and HDR10, which delivers more brilliant and vivid colors.

Unfortunately, according to Apple, the 4K High Dynamic Range stream requires a Mac introduced in 2018 or later.

The absence of 4K in Safari was a tiny sore point. Glad to see this evolution happening.