Netflix will only stream in 4K to Macs that have a T2 security chip
 

When Apple releases macOS Big Sur later this year, Mac users will finally have the chance to start streaming Netflix in 4K HDR on their computer. But you’ll need more than a 4K-capable display to do so. In a support document spotted by Apple Terminal...

https://www.engadget.com/netflix-4k-...205949278.html