As far as I know, last season Osimhen had a very large transfer market value which made many clubs unable to get him. Napoli also won't let other clubs get it easily. Because of that, they set a high price clause for Osimhen. This season Napoli's performance has been very bad. Osimhen managed to score 15 goals and was among the top scorers but was unable to provide a good performance for Napoli.
I think if given the choice in my opinion PSG is better than Napoli. They can almost always win the league so they will always be able to play in the UCL almost every season. But the problem is that currently PSG is not a good choice if you want to have a career. They are a good team but Ligue 1 is not as competitive as some of Europe's other top leagues.
PSG most likely have better contract terms, and I think better prospects in the Champions League than Napoli. If a football player feels that he wants to move on, then there is no point in keeping him. I don’t understand why PSG is a bad club for a career, they are the undoubted leaders in their championship, that is, this is an opportunity to get champion medals from another championship. In addition, they always strive to win the Champions League, and often get quite far. Of course, Ligue 1 is not as competitive a championship as the Premier League or La Liga, but you need to evaluate the capabilities of the club as a whole, and not just within their championship.