This filter is applied to use to get order count based on order status, it is including two parameters.
$order_count -> get order count.
$status -> order status.
An example of how you can append is below:
function count_orders( $order_count, $status ) {
$order_count = //count orders.
}
add_filter('rpress_order_count', 'count_orders', 10, 2);