Please get rid of blocking icon_prefix option
In Font Awesome 5 icon sets are specified with fal fa- far fa- etc.
In the iconFunction there's that line that puts %2$s (e.g. far) placeholder twice thus making it uselesss with FontAwesome 5
sprintf('<%1$s class="%2$s %2$s-%3$s"></%1$s>', $this->iconTag, $iconSet, $icon);
Ideally there should be only icon_class that would work with any icon font