A. No, because mandatory controls are owned by AWS Control Tower, and they apply to every OU on your landing zone. These controls are applied by default when you set up your landing zone, and they can't be deactivated. Moreover, none of them address RDS encrypted at rest.
B. Yes, because Strongly recommended controls are owned by AWS Control Tower. They are based on best practices for well-architected multi-account environments. These controls are not enabled by default, and they can be deactivated through the AWS Control Tower console or the control APIs. Moreover, three of them are RDS detective controls
C. No, because AWS Config does not create mandatory guardrails; AWS Config has managed and custom rules
D. No, because SCPs are created in AWS Orgs and are not designed to detect Amazon RDS DB instances that are not encrypted at rest.