What is the ruling on buying women's underwear from a male seller, and what is the ruling on buying it online when it is displayed by non-Muslim women, and is this considered an imitation of them?

There is no sharia impediment to conducting transactions, buying and selling, between a Muslim and a disbeliever, regarding what is permissible for a Muslim to buy and sell, unless it is known that the disbeliever will use these transactions to harm Muslims.