As far as I can see, your favicon is correct:
– It is properly declared in the HTML code.
– The links work (eg. https://science4fun.org/it/wp-content/uploads/fbrfg/apple-touch-icon-57×57.png)
– Your favicon is displayed correctly in IE 11, Firefox and Safari (Windows).
Yet, it fails on Chrome (both desktop and Android) and Opera (Windows).
I think this is because of the following code in the header of your HTML pages:
<div id=”fb-root”></div>
A div is not supposed to appear in the head section, but in the body section. When Chrome encounters this case, it (wrongly) considers the head section to be closed. And because the favicon declarations are after this div, Chrome think they are in the body and thus ignore them.
What you need to do is to find what is injecting this faulty div. Probably a plugin. Apparently, this is related to Facebook. Some Sharing buttons maybe? Ids I can see around are alvoiframe and sombrafbc. If one of them sounds like the name of one of your plugin, you probably found the culprit.
Once you know the plugin, you should contact its author. This div is a big, it can disrupt many other things, not just favicons.
And if none of the above works, you can deactive RFG’s plugin and install your favicon manually. Go to https://realfavicongenerator.net/ and follow the instructions of https://codex.www.ads-software.com/Creating_a_Favicon. Make sure to add the favicon code close to the top of the head section, else the same issue will occur again.
Does this help?