I think there is another reason why Napoli's president fired Spalletti after he won the Italy Serie A title for Napoli; it was not Spalletti's fault that Napoli was knocked out of the UEFA Champions League competition. Napoli was knocked out because Osimhen was not 100% fit to play for his club when he was needed most, and Napoli was knocked out. I believe Conte will not allow Osimhen to leave Napoli for any other club because he knows what he can achieve at Napoli if Osimhen remains at Napoli. Conte will need to strengthen his mild field and defense so that he can use his favorite formation without finding it hard to win matches when the Serie A league season starts.
Fired? No, Napoli didn't fire Spalletti. He wanted to leave by himself. Because he said that he was tired after such season and he decided to take some rest. Otherwise it would be absurd to see the chairman firing him after having an amazing season with him.
They must have tried their best to convince him for another season. I really don't remember such a solid season by Napoli for decades.They have changed many managers after him which is never a healthy way to get better. Because you just don't give that manager a proper amount of time to do better things. Anyways, it is at least still nice to see Conte there now. He is a really successful manager.