Explanation
To make an integration available for selection, a developer must create a RegisteredExternalService record using Workbench and create an Apex class that uses the integration framework. Creating a RegisteredExternalService record using Workbench allows the developer to register their custom integration class as an external service in Salesforce B2B Commerce. The RegisteredExternalService record contains information such as the class name, version, display name, description, and category of the integration class.
The category determines where and how the integration class can be used in B2B Commerce, such as ShippingService or TaxService. Creating an Apex class that uses the integration framework allows the developer to define custom logic for integrating with an external service provider's API or service. The integration framework provides interfaces and classes for various types of integrations, such as shipping, tax, payment, inventory, and freight. The developer can implement these interfaces and classes in their custom Apex class and override their methods with their own logic. Modifying the StoreIntegratedService to map to an Apex class ID using Workbench is not a required step for making an integration available for selection, as it is only used for registering internal services that are provided by Salesforce B2B Commerce out-of-the-box.
Entering the integration class name and version in store administration is not a required step either, as it is only used for selecting an existing integration class that has already been registered as an external service.
Salesforce References: [B2B Commerce Developer Guide: Integration Framework], [B2B Commerce Developer Guide: RegisteredExternalService Object]