add_action('wp_footer', function() {
    if (is_singular('post')) {
        $related = do_shortcode('[related-posts-by-taxonomy posts_per_page="3" format="thumbnails"]');
        if (!empty(trim($related))) {
            echo '<div id="related-inject" style="display:none">' . $related . '</div>';
            echo '<script>
            document.addEventListener("DOMContentLoaded", function() {
                var bloc = document.getElementById("related-inject");
                var nav = document.querySelector(".post-navigation");
                if (bloc && nav) { nav.parentNode.insertBefore(bloc, nav); bloc.style.display="block"; }
            });
            </script>';
        }
    }
});