I don't think Napoli would say okay to any kind of swap deal. They would rather accept cash for Osimhen and their demand would surely be insane amount of money. Arsenal aren't a poor team in the end. Their financial condition must still be solid despite spending a lot of money in the recent times.

If they are really keen on signing him then they had better make their move next summer. Napoli would try to extend with Osimhen until then. If they can't convince him for a new contract then there would be a big opportunity for Arsenal or any other team to take it.