Just finished adding "icons" for Decoding last week. Safari uses at least 3 type of icons on macOS and iOS together:

  1. one for pinned sites and web clips on your iOS home screen
  2. one for pinned tabs (which is an SVG by the way)
  3. and the usual favicon.ico.

And this is just Safari, I don't have icons for Windows or any other browser for that matter. Somebody should really provide a better way to deal with all that crap.