Side effects of not updating RDS certificate

No, there isn’t if your database is not using TLS encryption. The certificate authority is only relevant when SSL/TLS encryption is enabled between your application and the RDS database instance.

RDS provides the option to encrypt connections between your application and the database using SSL/TLS. When this is enabled, RDS uses a default AWS certificate authority to create the SSL certificates for the RDS instance. However, if SSL is not enabled for your RDS database, then TLS certificates are not being used at all. In this case, the certificate authority is irrelevant and does not need to be updated.

In case that you need enable it, please check this valuable blogpost: https://aws.amazon.com/blogs/aws/rotate-your-ssl-tls-certificates-now-amazon-rds-and-amazon-aurora-expire-in-2024/

Since your database is not using TLS, you can leave the certificate authority settings unchanged. Let me know if you have any other questions!