"The $changeStream stage is only supported on replica sets" error while using mongodb-source-connect

stage is only supported on replica sets

You need to make your Mongo database a replica set in order to read the oplog

https://dba.stackexchange.com/questions/243780/converting-mongodb-instance-from-standalone-to-replica-set-and-backing-up

MongoDB change streams option is available only in replica sets setup. However, you can update your standalone installation to a single node replica set by following the below steps.

1. Locate the mongodb.conf file and add the replica set details

Add the following replica set details to mongodb.conf file

replication:
  replSetName: "<replica-set name>"

Example

replication: replSetName: "rs0"

Note: Location in brew installed MongoDB /usr/local/etc/mongod.conf

2. Initiate the replica set using rs.initiate()

Login to the MongoDB shell and run command rs.initiate() this will start your replica set. Logs look like the following on successful start

> rs.initiate()
{
    "info2" : "no configuration specified. Using a default configuration for the set",
    "me" : "127.0.0.1:27017",
    "ok" : 1,
    "$clusterTime" : {
        "clusterTime" : Timestamp(1577545731, 1),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    },
    "operationTime" : Timestamp(1577545731, 1)
}

That's all with these two simple steps you are running a MongoDB replica set with one node only.

Reference: https://onecompiler.com/posts/3vchuyxuh/enabling-replica-set-in-mongodb-with-just-one-node