Install imagemagick:
brew install imagemagick
Creating the .ico file with multiple sizes:
convert favicon-16.png favicon-24.png favicon-32.png favicon-48.png favicon-64.png favicon.ico
magick convert favicon-16.png favicon-24.png favicon-32.png favicon-48.png favicon-64.png favicon.ico
- Image2icon (macOS app)
Tutorial: https://yoast.com/dev-blog/safari-pinned-tab-icon-mask-icon/
Clear Safari browser cached icons: ~/Library/Safari/Template Icons