Font Awesome uses font-display: block; in the font declaration of their more recent versions. This is because the Google Lighthouse project dings you in their automated accessability tool if you don't explicitly specify this.
It's not actually an accessability improvement I think, since the default behaviour is basically the same, but it's slightly nicer visually for the first visit to very slow loading sites, and it won't get flagged by accessability tester tools that check this is set.
They never added this to old versions, because they want you to upgrade, but we can add it ourselves to this file:
We just need to add
Similar to how FontAwesome do it for later versions:
Relevent upstream ticket: https://github.com/FortAwesome/Font-Awesome/issues/16077