According to [1] Netflix supports "Safari up to 4K on macOS 11.0 or later"

Of course, you also need to be on the 'premium' plan, have a fast-enough internet connection, be watching 4K content, have the T2 security chip, have an HDCP display, and so on.

[1] https://help.netflix.com/en/node/55764 https://help.netflix.com/en/node/23742

On Windows, you can, with a giant gotcha. Netflix need you to have all connect screen 4k to play ultra hd on Windows. I don't know if it is different if the screen is buildin.

On windows, I can play Netflix in 4K with HDCP 2.2, Windows 10/11 and the HEVC plugin from Microsoft.

Interestingly, if any montior you connect is not HDCP 2.2 you don't get 4K.

GeForce Stuff like Nvidia instant replay gets disabled if you have Netflix up in a tab - so close those before you game.