Hi, Good question
As per the documentation links provided in the question
rds-in-backup-planseems to be for the RDS database, so in other words DB backup
rds-resources-protected-by-backup-planis for the instances where the RDS is hosted, so in other words OS backup.
The difference seems to be in the Parameters of
Parameters: resourceTags (Optional) Type: String Tags for Amazon RDS instances for the rule to check, in JSON format. resourceId (Optional) Type: String ID of Amazon RDS instance for the rule to check.
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