Only using find method in mongo to limit filter age

I have the following BSON data:

[
  {
    "test": 1,
    "arr": [
      {
        age: 24,
        name: "a"
      },
      {
        age: 55,
        name: "b"
      },
      {
        age: 12,
        name: "c"
      },
      {
        age: 14,
        name: "d"
      },
      {
        age: 67,
        name: "e"
      }
    ]
  }
]

Is it possible by using only "find" method I get the output in a way that the "age" field inside "arr" array is less than 30 for each array element?.
So My expected output:

[
  {
    "test": 1,
    "arr": [
      {
        age: 24,
        name: "a"
      }
      {
        age: 12,
        name: "c"
      },
      {
        age: 14,
        name: "d"
      }
    ]
  }
]

If also it is possible with one find to flatten the array that would be great too.

Explained in the above.

>Solution :

You can use the $filter operator to filter the element(s) in an array in the projection.

db.collection.find({
  "arr.age": {
    $lt: 30
  }
},
{
  "test": 1,
  "arr": {
    $filter: {
      input: "$arr",
      cond: {
        $lt: [
          "$$this.age",
          30
        ]
      }
    }
  }
})

Demo @ Mongo Playground