Amazon RDS Proxy is compatible with Amazon RDS for PostgreSQL single-instance deployments. However, it doesn't support automatic routing to read replicas for non-Aurora PostgreSQL databases. This means that while RDS Proxy can manage connections to your primary RDS PostgreSQL instance, it won't automatically distribute read queries to any associated read replicas.

Source: https://repost.aws/questions/QURgpYNcQWQ32HmZ8lDLmS8w/rds-postgres-rds-proxy-read-replicas