"Order Duplicated" is an event that shows up in the "Activity" on an order.

An order is considered duplicated when a multiple orders are placed for the same delivery date. Any order placed after the first order for any one delivery date will get the "Duplicated by user" event in activity

What if I duplicate via "duplicate order" function on an order?

Even if an order is started from the "duplicate order" function it won't receive the "order duplicated" event unless it follows the logic above where it is a subsequent order placed for for the same delivery date.