Any way to insert fields only if they don't already exist in MongoDB?

I've tried some solutions i've found but im not getting how this is supposed to work (im new to mongo). i have a document that looks like this:

{
  "_id": {
    "$oid": "63ef95daf324e5a26354eb61"
  },
  "idCarga": "6182944",
  "12121212121212": {
    "info1": "hello",
    "info2": "goodbye"
  },
  "13131313131313": {
    "info1": "hello",
    "info2": "goodbye"
  }
}

My goal is to:

1. If i try to update the document with a new product ID field (like 15151515151515), it gets inserted as a new field.
2. If i try to update the document with an already existing prod ID (like 13131313131313), nothing happens (dont insert or update anything).

I got some results with the $exists operator paired with upsert option. But i have to insert so many product IDs it seems like an unviable option. Is there any way to do this with only one document per "idCarga"? Or do i have to separate this into 2 collections? Thanks in advance.

Simply do a $set with $ifNull

db.collection.update({
  <your criteria>
},[
  {
    $set: {
      "<your id>": {
        "$ifNull": [
          "$<your id>",
          {
            <your new sub doc>
          }
        ]
      }
    }
  }
])

Mongo Playground for new id case

Mongo Playground for existing id case