MacOS looks nice on either ~110dpi or ~220dpi monitor. Anything else and you get a blurry picture.
I have had similar blurring problems with a certain monitor (1920x1200 27"), which was resolved with changing some sharpening settings in the monitor itself. Strangely, that setting did not look well at my colleague's macbook, who was also often using that monitor, while the original settings looked fine, so we had to change the settings back and forth every time the other person had to use it. I do not think I was using zed at the time, other apps had that issue.
This is because macOS does not support subpixel rendering or hinting.