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 likely extending his contract with napoli. Read this
https://www.goal.com/en/lists/victor-osimhen-chelsea-napoli-transfer-new-contract/bltb068810c523b028eIMO, osimhen is likele trying to agree with the new contract and napoli will set a new release clause for him in the new contract. I have seen that how osimhen was complaining about the inconsistentcy of his club to determine how much release clause is worthy for him.
I remember napoli's president is always changing his decision regarding osimhen's price to buy him out from the club. Osimhen has requested the club to make everything clea and that's what he will get in the new contract.
Napoli needs to put the actual release clause for him. This is also the main requirement to make osimhen try to be in napoli much lonver. he really loves napoli, and he was not willing to go to the other club.
I saw it as a setback for him consider napoli will not make him to be a better striker. He was good but not comparable to the haaland.