Spoofing the user agent and decoding capabilities and [...] is a useful way to unblock things that are crippled on various browsers, indeed.
The problem here is requiring hardware-attested DRM: Widevine L1 on Edge on Windows, and Apple FairPlay on Safari on MacOS. The only way to get hardware attested DRM is via browser specific (i.e.: native code) support that interfaces with the OS & GPU drivers. You can't get there through an extension.
Right, but the point is that Netflix still refuses to play 4K on some browsers with hardware DRM support. Even getting it to work in Edge was a challenge last time I tried - iirc I got it working via https://github.com/lkmvip/netflix-4K-DDplus
The problem here is requiring hardware-attested DRM: Widevine L1 on Edge on Windows, and Apple FairPlay on Safari on MacOS. The only way to get hardware attested DRM is via browser specific (i.e.: native code) support that interfaces with the OS & GPU drivers. You can't get there through an extension.