In mongosh run: 
 
test> db.stats({freeStorage: 1});
MongoServerError: scale has to be a number > 0
 
Expected: 
Output similar to the runCommand call:
 
test> db.runCommand({dbStats: 1, freeStorage: 1});
{
 db: 'test',
 collections: 1,
 views: 0,
 objects: 1,
 avgObjSize: 36,
 dataSize: 36,
 storageSize: 20480,
 freeStorageSize: 0,
 indexes: 1,
 indexSize: 20480,
 indexFreeStorageSize: 0,
 totalSize: 40960,
 totalFreeStorageSize: 0,
 scaleFactor: 1,
 fsUsedSize: 46888751104,
 fsTotalSize: 62725623808,
 ok: 1,
 '$clusterTime': {
  clusterTime: Timestamp(

{ t: 1642786653, i: 1 }
),
  signature: {
   hash: Binary(Buffer.from("0000000000000000000000000000000000000000", "hex"), 0),
   keyId: Long("0")
  }
 },
 operationTime: Timestamp({ t: 1642786653, i: 1 })
}