It is like saying he is not for sale, and that means if Osimhen wants to leave, but not allowed to leave, all he will do is just wait until his contract is over and he will be fine to leave for free. That would be stupid of Napoli to do, just accept the highest offer PSG could go to, and then sell Osimhen, and buy Lukaku, and the rest can be used to make the team better.
If the situation is like this, Napoli will be very disadvantaged because Osimhen no longer feels comfortable playing with Napoli again because he feels the club is deliberately making it difficult for him to go to PSG. The interest from PSG has changed Osimhen's perspective on his future, he could get a place in the Champions League with PSG and win the Ligue 1 title there, while at Napoli he will have difficulty regaining the Scudetto like he previously achieved with Spalletti. Napoli need to consider the offer from PSG before it is too late, they can use the money to buy Lukaku and other players according to the team's needs.