The objects that will be created in Order Management when a customer orders a product through B2C Commerce but changes the quantity ordered after the Order Summary record is created in Order Management, and then returns one of the productsare:
A Return Order object. A Return Order is a record that represents a return request for an order or part of an order. A Return Order has a lookup relationship to both Order Summary and Change Order objects, and it contains information such as the return reason, status, date, etc.
A Change Order object. A Change Order is a record that represents a change request for an order or part of an order. A Change Order has a lookup relationship to the Order Summary object, and it contains information such as thechange type, status, date, etc.
Verified References: https://help.salesforce.com/s/articleView?id=sf.order_management_return_order.
htm&type=5 https://help.salesforce.com/s/articleView?id=sf.order_management_change_order.htm&type=5

Explanation
Two objects that are found within Order Management are:
Fulfillment Order. A Fulfillment Order is a record that represents a group of products in an order that are fulfilled together from the same location. A Fulfillment Order has a lookup relationship to the Order Summary object, and it contains information such as the fulfillment location, delivery method, status, etc.
Payment Summary. A Payment Summary is a record that represents a payment made for an order or part of an order. A Payment Summary has a lookup relationship to both Order Summary and Invoice objects, and it contains information such as the payment amount, method, status, etc.
Verified References:
https://help.salesforce.com/s/articleView?id=sf.order_management_fulfillment_order.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.order_management_payment_summary.htm&type=5

When a customer applies a discount when placing an order, an order adjustment group summary is created.
An order adjustment group summary is a record that represents a modification to the order amount,such as a discount, a surcharge, or a tax. An order adjustment group summary can have one or more order adjustments, which are the individual modifications that are applied to the order or the order items. An order can have one or more order adjustment group summaries, depending on how many types of modifications are applied to the order. References: Order Management Objects, [Order Adjustments]

Explanation
The required amount of test code coverage when deploying an Apex class is 75%. This means that at least
75% of the Apex code must be covered by unit tests, and all of those tests must complete successfully.
Verified
References:https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_deploying_ant_depl

The best way for an administrator to research the issue when a user is encountering an error when attempting to save an Account record is to use a user trace flag and debug log on the affected user. A user trace flag enables debug logging for a specific user, and a debug log captures database operations, system processes, and errors that occur when executing a transaction or running unit tests. The administrator can use these tools to identify the root cause of the error and fix it accordingly. Verified References: https://help.salesforce.com/s
/articleView?id=sf.code_add_users_debug_log.htm&type=5https://help.salesforce.com/s/articleView?id=sf.
code_viewing_debug_logs.htm&type=5