180 million is indeed too much for Osimhen. Mbappe was signed for that amount by PSG.

Of course the conditions of that time and now aren't the same. Players are getting more expensive in the transfer market now that we see even average level players being signed for really high amount of money. But I still don't think 180 million can be given just like that to any player. Osimhen is a really talented striker undoubtedly. But is he really worth the risk of paying a huge amount?
I don't think he is worth it now. He is still young and he needs to improve continually to prove his worth.
If his current market value and money placed on him by Napoli is compared to Mbappe market value then it’s probably worth it. But to end all of this, Napoli don’t want to let him go now that’s way a big price like this his placed on him. He happens to be the third most valuable striker in the world now but the consistency is what matters now to any team that is willing to have him by their side. No team will want to pay such huge amount and later not get what they deserve. There’s very high possibility that he’s going to remain at Napoli and this won’t be a bad decision for him to stay back.
And in fact Napoli had deliberately set high rates for Osimhen in the transfer market. This is done so that no team wants to buy him in the current transfer market. Because the Napoli Party realized that the Napoli Club was not ready to be abandoned by Osimhen. Losing the coach who has helped Napoli win the title in Serie A alone is a bad thing for the Club. Then it would be even worse if Osimhen left too. So setting high rates is a good plan made by the Napoli club management. Because if Osimhen turns out to be redeemed at that price. so with the funds received of that size it will allow Napoli to find a replacement which is also quite good with the large funds obtained from the sale of Osimhen. But fortunately at this time no club thinks that Osimhen is worth that price. so that no one dared to bring it. and the clubs that were rumored to be closing in on Osimhen have slowly backed down by now. So I agree that Osimhen will definitely stay at Napoli.
So far no team officially linked with Osimhen and considering the good performance he had in the last season that's weird to see no official offers for Osimhen, but as you said maybe that's because of the high amount of money they have to pay for him, otherwise, teams like Real Madrid and Bayern Munich could hire this player.
Indeed, there are not many official offers that are really serious about bringing in Osimhen. But issues about several big clubs being interested in Osimhen are indeed being discussed. but in reality there has been no official offer to bring Osimhen from Napoli. Because 180 million euros is a very high price. This is what has made many clubs withdraw and not be able to send an offer to the striker from Nigeria.
Recently there was also news about Liverpool being interested in getting the signature of the Napoli mainstay. But Liverpool have yet to make an official offer. So I think it's just going to be issues like other clubs do. who are only interested but apparently don't dare to pay a high price for Osimhen.