https://wccftech.com/safari-in-macos-big-sur-supports-netflix-streaming-in-4k-hdr/

Safari 14 in macOS Big Sur has gained support for Netflix streaming in 4K HDR quality, as long as you have a 2018 or later Mac. The 4K HDR streaming works even on Macs with smaller display sizes.

Netflix has offered 4K streaming for a long time but it has been limited to televisions and streaming devices which have support for both 4K resolution and HDR. Only Microsoft Edge and Netflix app on Windows 10 have supported Ultra HD 4K playback. Despite hardware support for HEVC codec, which Netflix uses, Apple had not built support in Safari for the video streaming service to enable the higher quality streaming.