I created a pixel-perfect template, including the grid and all export options, everything you need. So if you want to kickstart your macOS icon design, go to my Figma Community page and fork the file!
See as well:
Xamarin macOS Application Icons
A collection of macOS application icons I designed for Xamarin.
Please check out the application icons I designed for the Fork Git client: I used the template above as the starting point when I created the icon for Fork 2.0.