edit Assuming here that you are accessing the camera web GUI, as opposed to the NVR web GUI.
If it's the NVR - it's not powerful enough to handle the 4k stream either.
It's complaining about the inadequate PC performance.
What processor is in the PC?
The browser-free 'websocket' capability to render video in any browser is very heavy on the CPU.
You will find that the old IE11 with webcomponents plugin is much more efficient at rendering video, and should work OK on a limited power PC at 4k.
You'd be wasting the camera not using the camera's 8MP resolution.