Which solution will meet these requirements with the MOST operational efficiency?

Explanations:

Creating a function URL for the Lambda function allows direct HTTP invocation, making it easy for the third party to call the webhook with minimal setup. This solution is straightforward, efficient, and leverages native AWS functionality to handle incoming requests.

Using an Application Load Balancer (ALB) adds unnecessary complexity and operational overhead. While it could route traffic to the Lambda function, it is not needed since Lambda supports direct invocation through function URLs. This approach increases cost and maintenance without providing additional benefits.

Amazon SNS is designed for publishing messages to multiple subscribers, but it does not directly handle webhook calls. Providing a public hostname of an SNS topic to the third party would not allow the webhook to trigger the Lambda function efficiently, as SNS would require additional configuration and would not be the most operationally efficient solution.

Similar to SNS, Amazon SQS is a queue service that allows decoupling of components but is not intended for direct webhook calls. The third party cannot send webhook notifications directly to an SQS queue in a way that triggers the Lambda function without additional processing. This approach complicates the design and reduces operational efficiency.