Based on some changes in Universal Containers' Commerce engine, new Orders are expected to have two additional attributes at the header level. In Order Management, besides Order, the other object that also needsto be extended is Order Summary. An Order Summary is a record that stores information about an order, such as the total amount, the number of items, and the fulfillment status. An Order Summary is created by a process called Create Order Summary Process, which runs whenever an order is created or updated. The process calls a flow called Create OrderSummary Flow, which calculates the order summary fields and creates or updates the order summary record. To extend an object in Order Management, an administrator can create custom attributes on that object that match the API name and data type of the corresponding attributes in B2C Commerce. References: Order Management Objects

The type of relationship that exists between FulfillmentOrder and Order Delivery Method is Lookup (OrderDelivery Method). A Lookup field is a type of custom field that creates a relationship between two objects, but does not support rollup summary fields. In this case, a FulfillmentOrder has a Lookup field named Order Delivery Method that references an Order Delivery Method record. An Order Delivery Method is a record that represents a delivery option for fulfilling orders, such as standard shipping, express shipping, in- store pickup, etc. An Order Delivery Method can have many FulfillmentOrders associated with it, but a FulfillmentOrder can only have one Order Delivery Method. Verified References: https://help.salesforce.com/s
/articleView?id=sf.custom_field_types.htm&type=5https://help.salesforce.com/s/articleView?id=sf.
order_management_order_delivery_method.htm&type=5

The Status field on an Order Summary object is a picklist data type. A picklist is a field that allows users to select one value from a predefined list of values. The Status field on an Order Summary object indicates the current state of the order, such as Draft, Activated, Completed, or Cancelled. The values for the Status field are defined in the OrderStatus picklist field on the Order object. References: Order Management Objects,
[Picklist Fields]