Can you encrypt an existing unencrypted Amazon Redshift snapshot?

No, Amazon Redshift snapshots are encrypted together with the data at the same time your Amazon Redshift cluster is encrypted. However, you can encrypt a previously unencrypted cluster, but only the subsequent snapshots will be encrypted.

For more information, see [Encrypt your previously unencrypted Amazon Redshift cluster with 1-click] (https://aws.amazon.com/about-aws/whats-new/2018/10/encrypt-amazon-redshift-1-click/). Also, Amazon Redshift database encryption in the Redshift cluster management guide.