You are right that Osimhen is not interested in extending his contract with Napoli. This is why Conte is not interested in Osimhen now. He wants to add Lukaku to the squad. Because Napoli management will try their best to sell Osimhen this season. By selling Osimhen, Napoli management will earn a huge amount of money.
Osimhen is talented. He has managed to score a lot of goals in the last two seasons. Several big clubs like PSG, Chelsea, Arsenal and Manchester United are interested in adding a talented player like Osimhen to the squad. However, 130 million euros is a very high price. No club is interested in spending so much money. If it is 75-100 million Europe then maybe Napoli management can sell Osimhen this season. But the Napoli management is not interested in selling Osimhen for less than 130 million euros. Osimhen's future is still completely uncertain.
Victor Osimhen is a great player, a great warrior and a very generous person who spends himself.
But he rightly also wants to grow from a career point of view, so he wants to win something.
He's not trying to be rude to Napoli.
Then other disagreements with the team and the club damaged the relationship: it can no longer continue.
Better is a more mercenary and more docile player who knows how to score goals: Lukaku.