Need to disable the dropdown once the option is selected - google-apps-script

Question

Once the option in the dropdown is selected, that cell needs to be disable and no further changes it should permit.
Basically need to remove the edit rights for that particular cell once the option is selected or anything is entered in that dropdown cell(while dragging and filling the dropdown option).
SS Link: https://docs.google.com/spreadsheets/d/127P05KL1tzGru8PMXFLM57y20m1qOVnRS8IAfptsIh4/edit?usp=sharing
Since I am new to google script, I am sure it is possible but don't know the way out.

Answer 1

I believe your goal is as follows.
You want to protect the cell when the dropdown list of column "A" is changed.
In this case, how about the following sample script?
Sample script:
Please copy and paste the following script to the script editor of Spreadsheet and save the script. And, in order to run the script when the dropdown list of column "A" is changed, please install OnEdit trigger to the function installedOnEdit.
When you want to use this script, please change the dropdown list of the column "A". By this, the script is automatically run by the installable OnEdit trigger.
function installedOnEdit(e) {
const { range } = e;
const sheet = range.getSheet();
const dataValidation = range.getDataValidation();
if (sheet.getSheetName() != "Sheet1" || range.columnStart != 1 || !dataValidation || dataValidation.getCriteriaType() != SpreadsheetApp.DataValidationCriteria.VALUE_IN_LIST) return;
var protect = range.protect();
protect.addEditor(Session.getEffectiveUser());
protect.removeEditors(protect.getEditors());
if (protect.canDomainEdit()) {
protect.setDomainEdit(false);
}
}
When this script is run, the cell is protected. In this case, only the owner can edit the cell.
Note:
This script was tested using your provided Spreadsheet. When you change Spreadsheet, this script might not be able to be used. Please be careful about this.
References:
Installable Triggers
protect()