He's going to be a top striker playing for Manchester United, but I hope he'll be willing to wait for Manchester United to get things together before he start demanding the club gives him a major trophy as Manchester United aren't in a position to start competing for titles as they're yet to get the club in sharp. They have a new manager and it'll take some season for him to start showing strong contentions for the premier league title or even the champions league title but still, a move to Manchester United is going to be a great move and an upgrade for him from the club and league he's currently playing at. Napoli shouldn't sabotage this deal if Manchester United are serious about it.
If Manchester united are ever going to get another striker and are willing to spend €100m on one ( that's Osimhen release clause except Napoli brings it down) I think Amorim would want to bring Viktor Gyokeres from Sporting Lisbon with the same release clause, he's also as good as Osimhen but Amorim would like to work with him instead.
They already have Joshua Zirkzee and Rasmus Hojlund what else do they need a new striker for?
Zirkzee and Hojlund unfortunately fell short of expectations. Both Osimhen and Gyökeres are much better forwards than them. Hojlund, who they acquired from Atalanta, was an early transfer in my opinion. He was transferred to Manchester United before he had even proven himself. I couldn't show the performance he expected at Manchester United either. Since Manchester United had forwards like Rooney and Van Nistelrooy in the past, the fans are looking for forwards of this quality. Maybe Osimhen or Gyökeres can meet this expectation.