Creating columns across all the spreadsheet + transpose the data - google-apps-script

Question

I'm running API requests to export data from third party to a Google Spreadsheet.
This script will be running automatically on a weekly basis (for report purposes).
In this Google Spreadsheet, I need to:
Create columns across all the sheets (they are all structured in the same way).
Transpose the data from previous week to the newly created columns.
Delete the old data from last week in the sheet named 'raw data'
Hide this sheet name 'raw data'
I've created a script with the 4 tasks I need Google Sheet to perform.
I'm guessing there are some issues with my functions/constants in my following script. I just need one function that nests all the other needed 'subfunctions' inside.
A bit of help to fix this would be appreciated. I feel I'm almost there :)
function columnCreation() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sheet = ss.getSheets()[0,1,2,3,4,5];
const range = sheet.getRange('D1:H55').getValues();
const newrange = sheet.getRange('I1:M55');
const rules = sheet.getConditionalFormatRules();
const today = Utilities.formatDate(new Date(), "GMT+7", "MM/dd/yyyy");
sheet.insertColumnsAfter(8,5);
sheet.clearConditionalFormatRules();
sheet.setConditionalFormatRules(rules);
newrange.setValues(range);
sheet.getRange('D1').setValue(today).setNumberFormat("MMMM DD");
}
function clearAllContent() {
var range = SpreadsheetApp.getActive().getSheetByName('Raw Data').getRange();
range.clearContent();
}
function hideSheet() {
SpreadsheetApp.getActive().getSheetByName('Raw Data').hideSheet();
}

Answer 1

As an answer for the comment:
The error shown is on line 4 which refers to line 3 var sheets which is not a single sheet but an array of them.
To solve it you have to select which of the sheets you want to select. As an example, if there is only one Sheet, you have to choose 0:
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sheet = ss.getSheets()[0];
const range = sheet.getRange('D1:H55').getValues();