you can add your own class under post loop item,
add_filter('post_grid_grid_items_class', 'post_grid_grid_items_class_20200614', 10, 2);
function post_grid_grid_items_class_20200614( $class, $args){
$post_id = $args['post_id'] ;
$class .= 'new-class';
return $class;
}