Postgres doesn't have anything built in today, though a single node will comfortably scale to ... let's say somewhere between 100GB and 10TB depending on your use-case. Beyond that you can do read scaling with replicas, implement something with Foreign Data Wrappers, or hand-roll a sharding solution and stay on vanilla.

Alternatives to the DIY approach include open-source things like Postgres-BDR, CitusData, TimeScaleDB or closed-source single-vendor things Amazon Aurora, and RedShift.