How to fix the freight charges of sales order

When creating the sales order the shipping charge is calculated as a multiplication of the base price of the shipping and the item quantities.

Does anyone know of a workaround or a setup to implement in order to proceed with a freight charge price that is fixed and does not depend on the quantity? 

Below is an example if a line is composed of 20 quantities of the item XYZ I would like to find a method that considers me as a freight charge 5 euros and not 20*5

I also see that the Flat Rates tab in the update 24D doesn't work.