MongoDB Shema to support concurrent update on a document

Question

We were working on a project with a 300 documents with currentValue field in a main collection, in order to track the history of each document of first collection. we created another collection named history with approximately 6.5 millions of documents. For each input of system we have to add around 30 history item and update currentValue field of main collection, so, We tried computational field design pattern for currentValue, which lead us to have writeConfilict in concurrent situations (at concurrency of around 1000 requests).

Then we tried to compute currentValue field with sum (amount field) and groupBy(mainId field) on history collection which takes too long (> 3s).

Main collection docs:

{
    "_id" : ObjectId(...),
    "stock" : [ 
        {
            "currentAmount" : -313430.0,
            "lastPrice" : -10.0,
            "storage" : ObjectId("..."),
            "alarmCapacity" : 12
        }, 
        {
            "currentAmount" : 30,
            "lastPrice" : 0,
            "storage" : ObjectId("..."),
            "alarmCapacity" : 12
        }, 
       .
       .
       .
    ],
    "name" : "name",

}

History collection docs:

{
    "_id" : ObjectId("..."),
    "mainId" : ObjectId("..."),
    "amount" : 5,
}

If you have any other idea to handle this situation(application or db level), I would be thankful.

UPDATE 1

The update query if I use computed pattern would be:

mainCollection.findOneAndUpdate(
            {
                $and: [
                    { _id: id },
                    { "stock.storage": fromId },
                    { "stock.deletedAt": null }
                ],
            },
            {
                $inc: {
                    "stock.$.currentAmount": -1 * amount,
                }
            },
            {
                session
            }
        )

And Aggregation pipeline if I want to calculate currentAmount everytime:

mainCollection.aggregate([
            {
                $match: { 
                    branch: new ObjectId("...")
                }
            },
            {
                $group: {
                    _id: "$ingredient",
                    currentAmount: {
                        $sum: "$amount"
                    }
                }
            }])