you mean screen recording? Or using a virtual display you can record? pretty sure this is false for the level 1 DRM used for 4k content. Still certainly will work for some things but never for 4K. Sites downgrade you to 720p if you're in a lower security context. Would love to be proven wrong.

Use OBS to capture the 4K version of this test pattern[0] off Netflix and I'll buy you lunch!

You can point a camera at your monitor of course, but with level 1 DRM the video decoding happens in a hardware video decoder that's not accessible by the operating system. If you try to screen record or use OBS on 4K content on macOS/Windows, you just get black. Same with phones. It's not "just use OBS". If it works for you it's probably because you're getting 720p content. (which admittedly provides the majority of the value)

[0] https://www.netflix.com/title/80018499 # <-- this test pattern is the most reliable way to actually know what resolution video Netflix is sending you.