Your question is Integrating External Orders with Salesforce. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You want to display Order records on an Account related list, but the Order records sit in an external system. What is the best way to do that?
Asked in the first round stage. Explain the Salesforce product choice, relationship configuration, access pattern, and important limitations. Address what you would do if the external system cannot support the required Salesforce Connect protocol or query behavior.