Even the PSG rumors isn't certain because as of now there's actually no official update on the fate of osimien and I don't why you feel he can't go to Chelsea because from osimien view of things of himself he would love playing for a English side and also in the premier league, beside the English premier league is more competitive than the french league A.
There is no official announcement because PSG may be negotiating with Napoli and Osimhen. Chelsea scout is probably negotiating, too. So, there is nothing to be announced for now. Moreover, Napoli wants more than €100m for the transfer fees. It is a big amount of money, PSG and Chelsea shouldn't be easy to decide spending a lot of money for a single player only. Especially, a player who no longer plays in his best form.