Note there was an error in my math here which I can no longer correct. My 27" 4K at a distance of 20" has a PPD of 63, which is also considered retina. Compare this to the Vision Pro PPD of ~34.

To get true 4K res (3840x2160) at a PPD of 34 would require a screen that is 3840 / 34 = 113 degrees wide, way in excess of what is accessible by adduction of the human eye. A 60° wide screen would have a resolution of 60*34 = 2,040 pixels wide, or roughly 1080p.