Napoli could make such a move if the deal with Galatasaray falls through but I don't think Liverpool are too interested in Osimhen because if they really wanted him, they would have negotiated a player exchange with Nunez and Napoli would also benefit by getting Nunez + additional money from Liverpool, or maybe Liverpool want to wait for Osimhen to become a free agent, I don't know, I think Osimhen situation is quite complicated because he is having difficulty leaving Napoli until the current summer transfer window.
Basically Galatasaray would convince Liverpool instead of Napoli 
Like not even pay Napoli, just pay Liverpool, and get Nunez to Napoli and Osimhen to themselves that way lol. Because we all know, whatever Galatasaray pays, will go to Nunez probably, maybe a bit more money could be left.Last I saw from twitter, it's 5 year deal for 75 million, which would be 15 million a year, not a lot of money at all, definitely could be paid by Galatasaray considering it is not 75 million suddenly, just 15 upfront, and next 15 is next year, so it's fine. With that kind of payment deal, they can get him. Also, Liverpool could end up doing this fine as well, doesn't feel like it would be that bad, both of the situation a lot better for all three teams.
Liverpool do not seem to be interested in Osimhen, which is why they never mentioned him even when they negotiate the potential transfer of Darwin Nunez to Napoli, Liverpool have not linked Osimhen with the negotiations. The striker targeted by Liverpool is Alexander Isak, and perhaps Liverpool need to wait first until Darwin Nunez is sold because signing Isak will require a high amount of money.
Frankly, I'm a bit surprised why not many European teams are interested in Osimhen, though he is a good striker and I don't think Osimhen's fee is as high as it used to be. If no rivals are equally interested in Osimhen, it is likely that Galatasaray will get him.