So now, if they change their favicon to something within Google's guidelines, how long until Google shows the new favicon? That is unclear and there is no real way to notify Google that you made the change - yet.2
References
- https://yvoschaap.com/weblog/how_to_optimise_your_favicon_for_google_organic_results "How to optimise your favicon for Google's new organic results? - Yvo Schaap".
- https://www.seroundtable.com/google-penalizing-favicons-27636.html "Google Search Penalizing Inappropriate Favicons".
- https://support.google.com/webmasters/answer/9290858 "Define a favicon to show in search results - Search Console Help".