There is a difference between using a border radius on desktop and mobile. Currently, we use a 3px border radius on desktop and 6px on mobile.
The border radius for desktop is smaller intentionally because placing elements close to one another would cause a visual imbalance.
The most common example is a group of form elements with small spacing between fields. It’s clear at first sight that these fields would be less visually connected with 6px border radiuses than with 3px ones.