MongoDB Update Nested Object

I am trying to represent a grid structure within a MongoDB. I am having trouble updating a nested object. More specifically, the columns array located within the layouts rows row array element. I have created the following models:

layoutModel.js

const LayoutSchema = new mongoose.Schema({
    rows: {
        type : Array , "default" : []
    },
})

rowModel.js

const RowSchema = new mongoose.Schema({
    columns: {
        type : Array , "default" : []
    },


    user_id: {
        type: String,
        unique: false,
    },
    layout_id: {
        type: String,
        unique: false,
    }
})

columnModel.js

const ColumnSchema = new mongoose.Schema({
    column: {
        type : Array , "default" : []
    },

    user_id: {
        type: String,
        unique: false,
    },
    layout_id: {
        type: String,
        unique: false,
    }
})

I am able to find the layout associated with the current user, and then add a new row to the layout database object.

server.js

// database models
const Layout = require("./database/models/layout.js")
const User = require("./database/models/userModel.js")
const Row = require("./database/models/rowModel.js")
const Column = require("./database/models/columnModel.js")

app.post('/add-row', jsonParser, (req, res) => {
  User.findOne({ _id: req.body.profile_id })
    .then((user) => {
        const new_row = new Row({columns: [],}) //create new row database object
        new_row.save() //save object

        //find user's layout database object
        Layout.findOne({_id:user.layout_id}).then((layout) => {
          //found user's layout
          layout.rows = [new_row, ...layout.rows] //add new row to array of all the old rows
          layout.save() //save object
        })
    })
  res.send('Add row')
})

However, when I try to add a new column to the row within the layouts rows array it does not update in the database. I am not sure why.

app.post('/add-column', jsonParser, (req, res) => {
  User.findOne({ _id: req.body.profile_id })
  .then((user) => {
    //user is logged in so get the users layout
    Layout.findOne({_id:user.layout_id})
      .then((layout) => {
         //found layout
         for(let row in layout.rows){  
          let row_id = layout.rows[row]._id.toString()  //current row's id
          if(row_id === req.body.var_row_id){           //found row to add column to
           const new_column = new Column({column: [],}) //create new column database object
           new_column.save()
           layout.rows[row].columns = [...layout.rows[row].columns, new_column] //add new column to array of all the old columns
           layout.save()
          }
         }
     })
     
  })
})

Any advice is greatly appreciated.