When Dusan left the scenario was Lukaku who entered to replace that position, especially Juventus are also still monitoring Lukaku as a successor when Dusan goes to Chelsea. and this makes them benefit because Juventus don't bother too much if they release Dusan to Chelsea.
As for PSG, the possibility when they are eyeing Dusan is because they are still messing around with the status of Mbappe at the moment and I think when Mbappe does not leave this season then they will also reduce the option of looking for a striker so in this case PSG is still 50/50 especially seeing that they are also ready with a 150 million offer for Osimhen it indicates that they still have not decided who their main target is.
What you described now perfectly shows how much all of these transfers are interdependent. Everyone is waiting for what PSG is going to do with Mbappe, PSG thmselves are waiting for Mbappe and Real Madrid because they can't sign another player for 150 million if they don't know whether Mbappe will leave, and there are several more clubs who would either have some of their options become valid or invalid depending on what happens with players at other clubs. It even trickles down to Lukaku and Juventus Turin. I think Chelsea won't remain stubborn and they will let Lukaku go because they can't be interesting in having him sitting on the bench when he is not the type of player Pochettino likes to play with.
Thats right. In the end these are interconnected but still the focus may be between Mbappe and PSG as this could leave some transfers open if Mbappe leaves.
On the other hand this could also encourage some players including Dusan and Osimhen who are at Napoli.
But that only refers to a few for the case of Chelsea there might be a difference because with Mbappe leaving or not they will try to get Dusan if that is the best option from Pochettino but if Mbappe leaves and Dusan is one of the options for a replacement then maybe Chelsea should be prepared for the competition that will occur between them and PSG.