As long as Chelsea has not officially signed Osimhen, anything could still happen, you must not forget that in the transfer market things always happen that you never expected. Osimhen could turn towards PSG because he has the opportunity to play in the Champions League, he can also win trophies easily there because PSG has always dominated Ligue 1.
Chelsea is improving after the failure of this season, Pochettino was fired because he was unable to improve Chelsea performance even though he had brought in several classy players. It took Osimhen more than two years to win the EPL trophy with Chelsea because the new coach needed time to make Chelsea appear consistent and the level of competition was very competitive. Meanwhile, he has a great opportunity to win the Ligue 1 trophy with PSG because so far PSG has always won the domestic trophy.
I also think PSG has a much greater chance of getting Osimhen than Chelsea. Financial factors are bad luck and also PSG playing in the Champions League might be a consideration.
The difference between Chelsea and PSG is not only in terms of getting a domestic title there, but PSG is a team that is much more developed than Chelsea because the Chelsea team is currently in decline so it is difficult for a player to develop if a team does not have good progress.
I think that for a much better future career, Osimhen should choose PSG.