How can you say that it was Antonio Conte's decision to sell Victor Oshime? This is not correct truthfully. Antonio Conte had talks with Victor Oshime for him to stay with the club but he was serious about leaving the club for good after all the disrespect faced from Napoli. Antonio Conte said he has nothing to say about what happened between the player and the club last season.
I also don't understand how misleading information is spreaded this easy... Napoli simply mocked Osimhen through their social media. Later on he got really disturbed about it and things got more heated after that. I think Osimhen is absolutely right about his decision. Why would he want to continue to play and act like nothing happened? It wouldn't be reasonable.

But the more interesting thing is, he has still extended his contract until 2027. Just what?

What happened all of a sudden? How was he convinced? If you are determined to leave then don't do this.