‘At a Glance’ dashboard: combining infos

dashboard_glance_items is a filter hook, not an action hook. See here for an explanation of the difference.

Your at_glance() function doesn’t include the existing values, so only the items you return will be present in the At A Glance widget items.

Something more like this:

function at_glance( $items ) {
    $number_users = count_users();
    $text = $number_users['total_users'];
    $roles = $number_users['avail_roles'];
    
    $items[] = '<a class="users-count" href="users.php">' . $text . ' total users</a>';
    
    foreach( $roles as $role => $count ){   
        if($role == 'none'){
        } else {
        $items[] = '<span><a class="users-count" href="'.admin_url('users.php?role=".$role)."">' . $role . '( ' . $count . ' )</a></span>';
        }
    }

    $args = array( 'public'   => true, '_builtin' => false   );
    $post_types = get_post_types($args, 'object', 'and');

    foreach ($post_types as $post_type) {
        $num_posts = wp_count_posts($post_type->name);
        $num   = number_format_i18n($num_posts->publish);
        $text  = _n($post_type->labels->singular_name, $post_type->labels->name, intval($num_posts->publish));
        if (current_user_can('edit_posts')) {
            $glance="<a class="".$post_type->name.'-count" href="'.admin_url('edit.php?post_type=".$post_type->name)."">'.$num.' '.$text.'</a>';
        } else {
            $glance="<span class="".$post_type->name.'-count">'.$num.' '.$text.'</span>';
        }
        $items[] = $glance;
    }
    return $items;
}

add_filter('dashboard_glance_items', 'at_glance');

…might be closer to what you’re looking for. (I’ve combined your //second and //first code, and tried to get it to a point where it won’t throw a fatal error.)