related_post_element_link_attrs

You can add custom attributes for each link.

add_filter('related_post_element_link_attrs','related_post_element_link_attrs_20200126', 10, 2);

function related_post_element_link_attrs_20200126($elementIndex, $elementData) {

    $option_id = isset($elementData['option_id']) ? $elementData['option_id'] : '';


    if($elementIndex == 'post_title'){
        echo 'data-attr="hello-data"';
    }


}