I stumbled upon this rather nice article (archive.is backup for those not wanting to open Medium):
The article give some interesting background with scientific paper, and Steve Jobs’ request to Bill Atkinson in 1981.
To Jobs, rounded rectangles were friendly, and he insisted that rounded corners were already everywhere. Jobs took Atkinson for walk to show that his request was not mere aesthetic whim. A few rounded objects and a “No Parking” sign later, Atkinson was convinced.
The most important part is I found Displaperture, a small utility app to make your macOS display has rounded corners