Interesting solution! It shows at the "no favicon" image on the page tab (the dog-eared page icon) in the latest Chrome/Edge for me, not as a blank/clear icon. (I get that same result when I used GIFs that were invalid).
Thanks for letting me know. I probably have to tweak it a bit to make sure it's valid in all browsers.
While researching, I've found some fun things people have been doing using text and emojis in SVGs [0]
[0] https://lean8086.com/articles/using-an-emoji-as-favicon-with... [1] https://css-tricks.com/emojis-as-favicons/
So far, this is what I've come up with -