In the past few days, other people have spoken about it and the deal will be a thing ONLY IF Neymar will leave PSG.
To link the above in the past months we got rumors of Neymar joining the premier league or going to Arabia.
There are 2 possibilities Joao Felix will be with Atletico Madrid if at the end of the season Diego Simeone does not continue his career with Atletico Madrid his contract will expire in 2024 or even vice versa Joao Felix is not comfortable if Simeone renews his contract because he will not get a place in the starting. Now the decision is on management, Joao Felix is a long-term investment for Atletico Madrid they had spent a lot of money on him of course they are more careful in making decisions.
I think Atletico Madrid is only gonna consider if the offer is around 100m Euro at least as like you said Atletico Madrid has spent a lot of money on him and probably is the biggest transfer in Atletico's history so I am sure they are not gonna go for offers of 40-50m Euro (if arrives). About PSG interests, I would say after making so many signings are they still interested in another winger? and with that also willing to spend 80-100m Euros? - I would be amazed if that's the case. Let's see how Neymar situation goes for now as Neymar exit is still not confirmed yet.
About Felix future- I would say @Dewi Ares is right with the two possibilities but I would like to add one more- If Atletico receives a good offer that they think matches or is near to their valuation then I think Felix move can happen also.