By selling Osimhen, Napoli management wants to earn big amount of money. And that's probably why Conte isn't showing interest in Osimhen right now. Napoli won't have to spend a fortune on Lukaku. Moreover, Lukaku is a very talented player. If Conte uses Lukaku properly, Lukaku will be able to score a lot of goals.
Victor Oshimen has a fairly expensive selling price before his performance continues to decline and his price continues to decrease, the management wants to immediately release this player so that he can get a big profit and can buy player at a cheaper price. It is known that Victor Oshimen's current price is around 100 million euros, while Romelu's price Lukaku is around 40 million euros so the management can secure some profits to recruit more players if needed.
In my opinion, Lukaku's performance is also quite good. This player seems suited to playing in Serie A rather than in the EPL. In fact, he is the player who has contributed the most to Roma. If he was at Napoli, he could replace Oshimen's role if this player was really sold by the club.
If Victor Oshimen wants to be sold by the club then he should be sold as soon as possible so that the club can get good money for selling him. Now the star is in good enough form and he has been performing brilliantly for the past few seasons so he now has enough market value. But the big money his current club has announced to sell him is too much for this player. I don't think any club will want to buy him for 100 million. From what I know about the transfer market, I would say Victor Oshimen is not a €100m player at all. If a club is interested in taking him and his current club wants to sell him, he must lower his market value only if another club is interested in taking him.