Yes, that work for you on your current system. But using a icns file as the source for setting an icon, the icon (quality) can scale across devices & system versions.
So ultimately it’s more of creating an actual portable icon file.
Yet another plugin for 2 things: 1) change the global and per Post html lang attribute, and 2) easy cross-reference Posts with same content but different languages using Alternate Hreflang
https://en.m.wikipedia.org/wiki/Apple_Icon_Image_format