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;

}

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