Two ways that an administrator can query Order Summaries using APIs in Workbench are:
Platform API. The Platform API is a set of REST and SOAP APIs that allow developers to access data and functionality in Salesforce from external systems. The Platform API includes various resources and operations for querying, creating, updating, or deleting records in Salesforce, such as Order Summaries. The administrator can use the Platform API in Workbench byselecting the REST Explorer or SOAP Explorer tabs, and entering the appropriate request URL and parameters.
Composite API. The Composite API is a type of REST API that allows developers to execute multiple subrequests in a single HTTP request. The Composite API includes various resources and operations for batching, tree, sObject collections, or transactions in Salesforce, such as Order Summaries. The administrator can use the Composite API in Workbench by selecting the REST Explorer tab, and entering theappropriate request URL and JSON body.
Verified Reference: https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_what_is_rest_api.htm https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/resources_composite.htm

TheSingle Location High Volume sample flow and the Multiple Locations sample flow are two examples of how to implement order fulfillment with Order Management. The Single Location High Volume sample flow is optimized for performance and scalability, but it only supports one fulfillment location per order. The Multiple Locations sample flow supports multiple fulfillment locations per order, but it has lower performance and scalability. To support both high volume and multiple locations, an admin can download both sample flows from the Partner Community and make a blend between them, considering trade-offs such as complexity, maintainability, and customizability. Reference: Order Fulfillment Flows, Partner Community

When building a flow for multiple locations, an administrator should consider the following challenges:
Multiple locations will introduce nested loops which can make the canvas substantially larger. For example, a flow that handles multiple fulfillment orders per order and multiple fulfillment order lines per fulfillment order will need to loop through both levels of records. This can make the flow more complex and harder to maintain.
Multiple locations can lead to limit exceptions. For example, a flow that queries or updates a large number of records across multiple locations may hit the SOQL query limit or the DML statement limit. To avoid this, an administrator should use bulkified actions and optimize the flow performance. Reference: Order Fulfillment Flows, [Flow Performance Best Practices]