Which combination of steps will meet these requirements with the LEAST amount of operational overhead?

Explanations:

Creating an AWS Backup plan with rules for daily, weekly, and monthly backups allows for customized retention requirements, addressing the regulatory needs of the company. This centralizes backup management and reduces operational overhead.

Configuring an AWS Backup plan to copy backups to another Region ensures that the backups are replicated immediately, meeting the requirement for cross-region backup replication. This process is managed by AWS Backup, minimizing operational complexity.

While using an AWS Lambda function could replicate backups and send notifications, it introduces additional operational overhead compared to the built-in features of AWS Backup, which already provides these capabilities. Therefore, it is not the optimal choice for this scenario.

Adding an Amazon SNS topic to the backup plan allows for immediate notifications if a backup job fails, meeting the requirement for real-time alerts on backup failures without requiring additional custom development.

Amazon Data Lifecycle Manager (DLM) is suitable for managing EC2 instance snapshots but does not meet the full requirements for EFS and RDS backup management, making it less suitable for this comprehensive backup solution.

Setting up RDS snapshots does not meet the requirement for a unified backup solution or the need for a single source of backup status across the AWS environment. RDS snapshots would require separate management and do not provide a comprehensive backup strategy for the entire AWS environment.