How I'll get the orderId in EVENT_AFTER_COMPLETE_ORDER in craft commerce?

Question

I'll want to update an orderStatus in craft commerce after the order is complete for a specific (digital) pruduct type. To send an extra email with download links, confirm email is already send based on the default status. To do that I'll use an event like this, but how I'll get the orderId from the event, looks like this id is only in the private _lineItems. So I'll can't use $event->sender->orderId.

/**
         * update status
         *
         * @return void
         */
        Event::on(
          Order::class,
          Order::EVENT_AFTER_COMPLETE_ORDER,
          function (Event $event) {
            $order = \craft\commerce\Plugin::getInstance()->getOrders()->getOrderById($event->sender->orderId);
            if ($order) {
              $order->orderStatusId = 5; // order status ebooks send is 5
              $result = Craft::$app->getElements()->saveElement($order);
            }
          }
        );

==== UPDATE ====

Final working solution:

        /**
         * Update orderstatus to send downloads mail for digital products
         *
         * @return void
         */
        Event::on(
          Order::class,
          Order::EVENT_AFTER_COMPLETE_ORDER,
          function (Event $event) {
            $order = $event->sender;
            if (!$order->id) {
                return;
            }

            $digitalProductTypeIds = [8,9,10];
            $digitalStatusId = 5;
            $updateStatus = false;

            // Loop through lineitems and search for digital products based on productype
            foreach ($order->lineItems as $product) {
              if( isset($product->snapshot['product']) && in_array($product->snapshot['product']['typeId'],$digitalProductTypeIds) )
              {
                $updateStatus = true;
                break;
              }
            }

            // Update orderstatus id if digital products present in the order
            if($updateStatus){
              $order->orderStatusId = $digitalStatusId;
              Craft::$app->getElements()->saveElement($order);
            }
          }
      );

Answer 1

Since it's a property-read, you can't do it with Order as an element, but you can try to deal with it via recorders, something like that

use yii\base\Event;
use craft\commerce\elements\Order;
use craft\commerce\records\Order as OrderRecord;
// ...

    Event::on(
        Order::class,
        Order::EVENT_AFTER_COMPLETE_ORDER,
        function (Event $e) {
            $order = $e->sender;
            if (!$order->id) {
                return;
            }

            $orderRecord = OrderRecord::findOne($order->id);
            if (!$orderRecord) {
                throw new \Exception('Invalid order ID: ' . $this->id);
            }

            $orderRecord->orderStatusId = 1337;
            $orderRecord->save();
        }
    );

If it doesn't work with this event, try using the event Order::EVENT_AFTER_SAVE