Mongodb $lookup in pipeline of aggregate function is slow in Atlas Function

MongoDB Atlas App Services & Realm Atlas GraphQL API
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I implemented a custom graphql resolver which does a series of pipelines inside aggregate function. When I execute it , it takes about 20 seconds. I thought it was because of deployment of regional vs global but I changed it and it is still the same.

I tried running same thing in mongosh which gave me result pretty fast with the instance of $cursor.

Then I changed my pipelines to only include search and match condition which works pretty fast. So I thought its because of the sorting and $lookup. I tried to keep only one and try which made the query slower. Finally I thought may be it is because of the database client that MongoDB Atlas provides from graphql is not native.

Here are the pipeline code that I tried.

const cluster = context.services.get("mongodb-atlas");
const items = cluster.db(DATABASE).collection(collection);
const pipeline = [
    searchCondition, // for search index query
    { $match: conditions }, // for the default where clause conditions
    ...item_details_join, // contains $lookup
    ...item_extends_join,  // contains $lookup
    sorting, //default sorting by the attribute descending
    { $skip: skip },{ $limit: limit },  // pagination
  ]
  .filter(
    (f) => Object.keys(f).length > 0
  );
console.log(JSON.stringify(pipeline,null))
return items.aggregate(pipeline).toArray();