Learn how to assign data validation using Apps Scripts and create dynamic dependent dropdown lists for the whole column for Google Sheets.

function onEdit(){
  var tabLists = "lists";
  var tabValidation = "Main";
  var ss = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var datass = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(tabLists);
  
  var activeCell = ss.getActiveCell();
  
  if(activeCell.getColumn() == 1 && activeCell.getRow() > 1 && ss.getSheetName() == tabValidation){
    
    activeCell.offset(0, 1).clearContent().clearDataValidations();
    
    var makes = datass.getRange(1, 1, 1, datass.getLastColumn()).getValues();
    
    var makeIndex = makes[0].indexOf(activeCell.getValue()) + 1;
    
    if(makeIndex != 0){
    
        var validationRange = datass.getRange(3, makeIndex, datass.getLastRow());
        var validationRule = SpreadsheetApp.newDataValidation().requireValueInRange(validationRange).build();
        activeCell.offset(0, 1).setDataValidation(validationRule);
  
     }  
      
  }
  
}

Understand How This Script Works