What is the MOST operationally efficient solution that meets these requirements?

Explanations:

An Amazon EventBridge rule with an event pattern for Amazon S3 would trigger the Lambda function on specific S3 events, such as object creation or deletion, rather than at a specific time each day. This does not meet the requirement to run the function at the end of each day.

Creating an Amazon EventBridge rule with a schedule allows the Lambda function to be invoked at a specified time daily. This solution is operationally efficient as it directly meets the requirement to generate a report at the end of each day without additional infrastructure or maintenance.

S3 event notifications are designed to trigger actions based on changes in the S3 bucket, such as uploads or deletions. This option does not fulfill the requirement to run a Lambda function at the end of each day since it is event-driven rather than time-based.

Deploying an Amazon EC2 instance with a cron job introduces unnecessary complexity and operational overhead. It requires managing and maintaining an EC2 instance, which is less efficient than using EventBridge for scheduling Lambda invocations. Additionally, it does not inherently provide the required daily schedule without manual configuration.