AWS RDS proxy dual read replica

Hello.

Do you want to create a read replica of an RDS PostgreSQL instance and configure RDS Proxy on the read replica?
In that case, although it is also described in the following document, it cannot be supported.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/rds-proxy.html#rds-proxy.limitations

For RDS DB instances in replication configurations, you can associate a proxy only with the writer DB instance, not a read replica.

If you don't mean that and simply want to add a read replica, I think you can add it by following the steps in the document below.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PostgreSQL.Replication.ReadReplicas.html