If the most important thing for Osimhen and Napoli is earning more money he can join the Saudi League where Osimhen can be sure about earning money and Napoli will earn enough to hire other players to take his place because we know other teams in Europe will not spend this huge amount of money.
In my opinion, Osimhen will relatively stay with Napoli because so far no team is really serious about signing him other than just saying they are interested. Napoli will have to keep their star players with them for next season if they want to strengthen themselves as the strongest team in Serie A next season.
To be honest If osimhen wants to chase money then he joins Saudi Arabia league Team in this Transfer market. I think that Osimhen will not do this because given his young age, of course he wants to win many trophies in prestigious leagues in Europe. Apart from that, the big European teams that are able to bring in Osimhen are most likely Real Madrid and PSG.