Ronaldo still talented player and I don't thing Napoli will get trouble if sign in Ronaldo in next window transfer open, actually have positive impact side if Napoli want to sign in Ronaldo due merchandise and Ronaldo's shirt will sold out fantastic depend on several team before with Real Madrid, Juventus and Manchester United become most sold Ronaldo shirt. Have slowly rythm I think Ronaldo doesn't need adapt with Serie A culture and become easy how to get in Splatti scheme games play.
But Napoli won't to sign in Ronaldo if his contract not break the contract with Manchester United in January, actually Ronaldo have several months left contract with Manchester United until June 2023 and seems not any one club interested to sign in him if not be free transfer player.
What about the salary that Ronaldo wants the same as at Man United? Of course it will be difficult for Napoli to pay for it unless there is a clause where Ronaldo is willing to do whatever Napoli offers him, apart from all that the Serie A game scheme is different from the Premier League then Ronaldo's contribution at Napoli will be seen if he moves to Serie A.
Ronaldo's fans are so many around the world that about merchandise and other t-shirt sales it will benefit the team because there is an attraction from Ronaldo, all the advantages he has, so regardless of the game, at least he has ambition despite his old age.
Regarding the Splatti game scheme, Ronaldo must be able to adjust it, maybe he will become the starting eleven or stay on the bench.