I was once asked to add a Favicon icon to phpBB so that it would be displayed in search engines and would look better, I will show you how to do it.
First, save the favicon.ico icon file to the forum root. There are online services on the Internet where you can convert an image to ico.
Then open /styles/ixnfo.com/template/overall_header.html of your active theme in a text editor.
And before the head tag, we add a link to the icon:
<link rel="shortcut icon" href="https://forum.ixnfo.com/favicon.ico" />
Done, you can also clear the cache and wait for search engines to index it. For example, after a couple of days, the icon appeared in Google search results.
See my other articles about phpBB