Take a final snapshot of Amazon RDS even if you retain automated backups

"Final snapshots are independent of retained automated backups. We strongly suggest that you take a final snapshot even if you retain automated backups, because the retained automated backups eventually expire. The final snapshot doesn't expire."

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithAutomatedBackups.html#USER_WorkingWithAutomatedBackups-Retaining-RetentionPeriods