Wow. Osimhen is playing his own game. First when he caught the eye at Napoli he didn't want to leave too soon, then he didn't want to stay, then he went on loan and now he wants to go to United whose only chance of getting into the Champions League is to win the Europa League. He would be a major boost for the club and as a United fan I welcome it but I can't see why he would take such a risk personally.
Osimhen just wanted to stay away from Napoli as quick as possible. It resulted in an opportunity for Galatasaray on loan.

However this summer he should absolutely sign for a team playing in a much bigger league like the Premier League.
I mean his market value has been decreasing for a long time. According to the graph below,
120 million euros => 70 million euros... He says he likes to play for Galatasaray these days. But if he doesn't want to throw his career aside, he should leave ASAP.

I don't trust these charts much - especially the section where the price has risen sharply in a short time is questionable. He is not getting cheaper, but returning to normal (and he is still a very expensive player and his price reflects his value).
That surge was caused by the situation when Bayern was trying to get Kane, Real Mbappe, the Saudis were also nearby, plus there was not much choice on the market. The fight between several top clubs for a limited resource drove up prices on everything.