Napoli no longer want Osimhen since last season so I'm sure he will move in the next transfer window especially since his contract ends this year and Napoli don't have many options, let him go for under market value or for free. Cunha might be another alternative but it would be no problem if Manchester United brought in these two players they need some strikers as alternative especially if the rumors of Højlund's transfer are true, reportedly clubs from Italy interested in him.
Manchester United are considering several alternatives in the attack line and maybe if the Cunha and Osimhen duet is realized, then next season there will be a surprise that we can see in the Manchester United squad. At present Amorim is quite serious in fixing the team because they are approaching some of the players needed and negotiations may run faster before the transfer market is opened.
Osimhen's contract in Napoli is almost over and if Napoli do not release immediately then they will not get anything. There is no beneficial option for Napoli and indeed they should release Osimhem so they can use money from sales to find the players they need.