Just finished adding "icons" for Decoding last week. Safari uses at least 3 type of icons on macOS and iOS together:
- one for pinned sites and web clips on your iOS home screen
- one for pinned tabs (which is an SVG by the way)
- 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.