Amazon Relational Database Service (Amazon RDS) for PostgreSQL, version 11 and higher, now supports M6i and R6i instances. M6i instances are the 6th generation of Amazon EC2 x86-based General Purpose compute instances, designed to provide a balance of compute, memory, storage, and network resources. R6i instances are the 6th generation of Amazon EC2 memory optimized instances, designed for memory-intensive workloads. Both M6i and R6i instances are built on the AWS Nitro System, a combination of dedicated hardware and lightweight hypervisor, which delivers practically all of the compute and memory resources of the host hardware to your instances.
Source:: Amazon AWS