On https://www.mongodb.com/docs/v4.4/core/sharded-cluster-components/#sharded-cluster-components we see (correctly) that:

A MongoDB sharded cluster consists of the following components:

• shard: Each shard contains a subset of the sharded data. As of MongoDB 3.6, shards must be deployed as a replica set.

However on https://www.mongodb.com/docs/v4.4/sharding/#sharded-cluster we see:

A MongoDB sharded cluster consists of the following components:

• shard: Each shard contains a subset of the sharded data. Each shard can be deployed as a replica set.

An issue came up in SERVER-69517 where a user brought up this inconsistency and how it can cause confusion. I'm not sure if there are other locations that should be updated, but we should have this note anywhere that setting up shards is mentioned:

• As of MongoDB 3.6, shards must be deployed as a replica set.