Adding to fontawesome-webfont.woff2 to boost website speed

If your theme is any good it will use wp_enqueue_style to include fonts in the head of your site. This gives you access to the style_loader_tag filter, which you can use to modify the html of the font link. Like this:

add_filter( 'style_loader_tag','wpse366869_preload_styles', 10, 4 );
function wpse366869_preload_styles( $html, $handle, $href, $media ) {

    // do this only when 'fontawesome-webfont' is mentioned in the html
    if( 0 != strpos( $html, 'fontawesome-webfont' ) ) {
        $html = str_replace( '<', '<rel="preload "', $html );
    }
    
    return $html;
}