In your script, as one of several possible modifications, how about the following modification?

From:

var tableData = [];
var table = document.getElementById("dtable");
console.log(table)

for (var i = 0; i < table.length; i++) {
  let tableCells = table.rows.item(i).cells;
  let cellLength = tableCells.length;

  for (let j = 0; j < cellLength; j++) {
    let cellVal = tableCells.item(j).innerHTML;
    tableData.push(cellVal)
  }
}
console.log(tableData)

To:

var table = document.getElementById("dtable");
console.log(table)

var [, ...tr] = table.querySelectorAll("tr");
var tableData = [...tr].map(r => {
  var td = r.querySelectorAll("td");
  return [...td].map((c, j) => j != 3 ? c.innerHTML : c.querySelectorAll("select")[0].value);
});
console.log(tableData)

• In this modification, from a table, the table rows are retrieved. And, the table cells are retrieved from the table rows. In teh case of the dropdown list, the value is retrieved from the dropdown list.

Note:

• When this modification was not the direct solution to your issue, I think that when you provide your whole script, it will help to correctly understand your question.