How to solve the browsing blur under Rentina screen of Macbook?

Retina technology itself is to display a point with four pixels, which can ensure that the font and UI displayed on the screen above UFHD will not be too small. As for your theory of this problem, it is not caused by the retina, but the resolution of your image is too low, and the dpi (dots per foot, one point represents one pixel) is too low to watch. From your description, the dividing line is about dpi 150. You said that when you took photos, the photos you took were not as high as those taken by your mobile phone, so you couldn't see them with dpi 150. Then I can only doubt that your ISO tone is not good, and the noise is too high.