In my opinion, Arsenal appeal is only lost in the Champions League, because they are not favored as title contenders. It is unlikely that Osimhen will join Manchester City, because Pep Guardiola has some pretty good players in the same position. Chelsea and Manchester United I don't think can offer anything in the near future, maybe Osimhen will think twice before joining them.
Joining Liverpool might be a better option, but so far there has been no news linking Osimhen with Arne Slot squad. Napoli have more power in negotiating Osimhen future, and of course they will push their asset away to a club who dares to offer a higher price. It would be a surprise if Osimhen ends up joining Manchester United.
I'm not sure Osimhen will choose Manchester united as his next team because he will choose a team that will compete in the Champions League. Arsenal is very likely to recruit him because arsenal needs a goal-hungry striker and osimhen can be arteta's choice to cover the gap in the front line.
However, will Arsenal be ready to spend a lot of money to recruit osimhen because Napoli will not agree if the offer that comes is below the release target they want. For that, arteta must focus on finding a way for them to recruit osimhen because Arsenal does lack competitiveness in the front line, even if the gap is not fixed, their hopes of becoming champions could always disappear every season.
If given the chance, Arsenal could take him on loan at the very least if they don't want to buy him for a huge amount of money. But at MU I'm pretty sure he won't make the move either. I think the point is that even though MU has top players, the team can't play adequately even with top players and apparently it's not about the coach, it's about the mentality of the team itself. In any case he doesn't belong there, he will ruin himself in this team