The named Ranged attached to the drop down is called Supplier and what I would like is that if a Supplier is added manually in the cell because it currently does not appear, then that entry is added to the named range so that next time the user clicks another drop down with that named range, it will appear
that kind of defeats the purpose of data validation, where you pick valid options from a list.
If people can enter their own values, then you will invariably end up with wrong spellings of suppliers that already are in the list. If you have "Apple" and "Microsoft" in the list and allow typing any other values, someone will come along and manually type "Micorsoft" and there's nothing you can do to prevent that.
Unless you keep the list of valid entries safe and add new valid entries to the list before they can be used in the data validation.