GraphCommerce offers a magento-graphcms example that provides an approachable path to building GraphCommerce custom e-commerce storefront.
Included in the magento-graphcms example, is a well-founded implementation ↗ for a correct favicon and touch icon.
Favicons can be found in the /public directory:
/public/favicon.ico /public/favicon.svg /public/apple-touch-icon.png /public/manifest/favicon-512.png /public/manifest/favicon-192.png
To replace the favicon with your own, simply replace the image files located in the /public and /public/manifest directories. Pay attention to the standardized "minimum safe zone ↗"
You can use the GraphCommerce favicon sketch template ↗ to simplify the process of making correct favicons.