Get onEdit to trigger from a single cell change - google-apps-script

Question

I am trying to run a Google App script that unhides columns, and then rehides columns based whether the cell reference says Blank or not. This is determined by a drop down in a single cell. I got the script to run fine (if a little clunky) whenever any edit is made, but when I try to add the specification of cell it flags an error with the range.
I'm very new to this so I'm a bit out of my depth so any help is appreciated!
function onEdit(e) {
if (e.range.getA1Notation() === 'B2') {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = SpreadsheetApp.getActive().getSheetByName("Group M0 loot");
sheet.showColumns(9, 35);
var range = sheet.getRange("4:4");
var num_cols = range.getNumColumns();
for (var i = 9; i <= num_cols; i++) {
var value = sheet.getRange(4,i).getValue();
if (value == "Blank") {
sheet.hideColumns(i);
};
}
}
}

Answer 1

Try this:
function onEdit(e) {
const sh = e.range.getSheet();
if (sh.getName() == "Group M0 loot" && e.range.columnStart == 2 && e.range.rowStart == 2) {
sh.showColumns(9, 35);
sh.getRange(4,1,1,sh.getLastColumn()).getValues().flat().forEach((c,i) => {
if(!c) {
sh.hideColumns(i + 1);
}
});
}
}