In the past I've used www.favicon-generator.org to create my favicon packages. It does it pretty well and includes app icons of all different sizes very similar to the favicon_package.zip that is in Nop 4.20. Is there a favicon generator that Nop used to create the default sample? If there is indeed a place to have it create the package, that would save on manually creating the zip to import via the new favicon admin upload.
ps. I did attempt uploading my own favicon.zip generated by the above site, but getting the error that html_code.html could not be found. Looks like all the default files from /icons/icons_0 were removed, including the html_code file.