Create an automation rules for manufacturing orders, with "on save" trigger, and select the "id" on "When updating"  field, this will trigger only when the MO is being created

edit the product_qty with this code

record['product_qty'] = round(product_qty * 1.1)

assuming that the item is only whole, otherwise remove the round function

note this this will have an issue if you implement an auto-replenishment