According to Debezium documentation[1], on AWS RDS, the rds_replication role is enough to read the wal_log. However, on the connection validation step, this case is omitted and the connector cannot start[2].

[1] https://debezium.io/documentation/reference/1.8/connectors/postgresql.html#postgresql-on-amazon-rds

[2]https://github.com/debezium/debezium/blob/main/debezium-connector-postgres/src/main/java/io/debezium/connector/postgresql/PostgresConnector.java#L105