Order post by modified date - Wordpress

functions.php

// Order post by modified date
function dfw_query_orderby_modified($query) {
    if (is_home() || is_home() && is_paged()) {
        $query->query_vars['orderby'] = 'modified';
        return;
    }
}
add_filter('pre_get_posts', 'dfw_query_orderby_modified');