Osimhen must move to a team that can offer him the chance to win trophies. I doubt if he wants to move to Chelsea although Chelsea can pay him more expensive than other teams. Chelsea is just a mediocre team in EPL, Osimhen won't expect any trophy with Chelsea.
First of all, Osimhen's contract with Napoli runs until 2025. It won't be easy to transfer him before 2025 because he is one of the best along with Mbappe and Haaland and the Napoli president rejected all offers for him in the summer transfer window. However, according to media reports, if Real Madrid can't sign Haaland or Mbappe, they will try to sign Osimhen as a plan C. I think this is a possible scenario because Real Madrid need to sign a striker of this class. So, I think there will be many alternatives for Osimhen in the transfer window. Everybody wants to sign a striker like him.
Osimhen is a quality striker, there is no doubt about that. I don't think he is the primary option for Real Madrid. Haaland would be a great option for Real, but my preference would be Mbappe. He has a structure that can play both as a forward and as a wing. Haaland plays as a complete finishing striker. While Mbappe makes it easier to intervene in the game, you cannot remove Haaland from his position.