Ah, but the question posed was "Name one artifact that we couldn’t produce."
You're moving the goalposts. These artifacts can't be produced today with our technology. Of course you can begin a Manhattan-project endeavor if your pockets are deep enough for the billions or trillions of dollars required in order to duplicate artifacts of the type that can't be figured out now. Just try to do it today. Without saying it is possible but we don't currently know how. Of course it was done millennia ago and they exist. That isn't the question. The question is how did the ancients get it done, and what tools did they possess to get it done.
Point me to the link that shows such an artifact. I am sure they can be produced today.