RDS Backtracking

Hello.

As stated in the document below, backtracking can only be enabled when creating a cluster or restoring from a snapshot, so I don't think it can be enabled on an existing cluster.
As of November 2024, the only way to enable backtracking on an existing cluster is to enable it when restoring from a snapshot or when creating a new cluster.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Managing.Backtrack.html#AuroraMySQL.Managing.Backtrack.Limitations

Backtracking is only available for DB clusters that were created with the Backtrack feature enabled. You can't modify a DB cluster to enable the Backtrack feature. You can enable the Backtrack feature when you create a new DB cluster or restore a snapshot of a DB cluster.

So, try creating a new cluster or enabling backtracking when restoring from a snapshot.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Managing.Backtrack.Configuring.html

Currently, you can modify backtracking only for a DB cluster that has the Backtrack feature enabled. The Backtrack section doesn't appear for a DB cluster that was created with the Backtrack feature disabled or if the Backtrack feature has been disabled for the DB cluster.