Inspired by @rafa’s https://docktor.site, I created Squircle - a free Mac app that adds the correct corner radius, padding, and shadow to square app icons following Apple's design guidelines. Just drop the square icon in and out you get a single png or an appiconset for Xcode.
https://apps.apple.com/us/app/squircle-resize-app-icons/id6499279814



