Yeah Osimhen prefers to stay and extend his contract with Napoli this means that Osimhen cannot make a decision in the next few seasons, unless Napoli wants Osimhen released, as you said, Osimhen's performance has not been optimal this season so his interest and market value will definitely decrease so there is a possibility that we will see Osimhen play longer in Serie A. This season Osimhen only scored 12 goals and this is proof that its performance is declining but Osimhen is still young he still has a chance to improve his performance next season.
At the end of December Osimhen has officially extended his contract with Napoli until 2026, and so far it is reported that Osimhen has a release clause of 130 million euros for teams outside Italy who want to sign Osimhen, although Osimhen has extended his contract with Napoli but I think his chances of leaving are still very big considering Napoli's position which is currently bad, In addition, with a release clause of only around 130 million euros, of course, it will not be difficult for PSG to fulfill it, in my opinion Napoli will have no chance of keeping Osimhen next season if indeed PSG really want to sign him.
Currently Osimhen continues to be contested by several Premier League teams but in my opinion PSG are the frontrunners to sign him, reportedly currently PSG and Napoli are in further talks about the transfer, so it is very likely that next season Osimhen will play at PSG and even PSG are ready to sign osimhen for 4 seasons worth €13 million (£11 million/$14 million) per season.