how to adjust freight charges with inventory cost when freight or shipping cost has nothing to do with the supplier all expenses are paid by the company, but definitely the actual cost of item for the company is the cost after paying the expenses on the item
additionally I have read the guides for freight in charges but it increases the total purchase invoice for the supplier to be paid.
Did you read the correct guide?
It is clearly explained here Add freight-in to inventory item costs | Manager how to handle separate freight only invoices and allocate them to the inventory products