Is it possible to use RDS for Postgres read-replica only in direct-connection?

I couldn't find answer to this question in the official docs, so hoping it isn't a stupid question. I have RDS for Postgres which is being used by multiple micro-services. One such service is the BFF and it requires a much better performance in terms of read latency, as it is used to serve data to the UI (it only reads), while other services are doing background jobs and are much more agnostic to slow queries and such. I had a thought, which I'm not sure makes sense, of adding a read replica, and make my BFF service connect directly to this read-replica, this way I can both create isolation from other services and make sure they don't affect the BFF performance and it also allows me to provide more resources (i.e. stronger read instance) only to the service that really needs it. I think that in Document DB this approach won't work, as any application that is connected using the cluster endpoint i.e. to the primary (and I must have at least one such app as it is the only way to perform "write") might end up running the read queries on any read replica, and I can't really enforce giving dedicated read replica to a service. I wonder if the same is true for RDS for Postgres or if that isn't the case and I can have a certain application using a single read replica exclusively.