Despite the fact that Victor Osimhen doesn't have a certain release clause in his current contract with the club, Napoli still wants to make over 150 million Euros should the Nigerian striker leave the the club this summer transfer window.
The club's reluctancy not to let the player leave without a huge transfer fee is because of the player's current striking power. It'll be difficult to find his replacement if he leaves now so they need a fee that can give them the financial strength to get a replacement
Look at that in all honesty he's worth them all, if you look at how many goals he's scored. Just to mention, Benzema Ballon d'Or has scored fewer goals than him, in an easier league (in the sense, scoring is easier in LIGA)
So they are right to sell it at that price.