By taking on a vendor's tool, I would argue you trade off ease for understanding.

If you truly need to shard, it's best to move deliberately and potentially roll your own at the application level. Your understanding of the infrastructure is far more important than sharding for the sake of sharding.

The author is a contributor to Apache ShardingSphere. https://github.com/apache/shardingsphere

Citus is probably the best way to do it today as it will handle most of the work for you.

Postgres uses table partitions for sharding, potentially combined with FDW to a remote database. The Postgres docs describe these features.

Citus. Built from scratch to make this as easy as possible.