I also don't think the rumors of Osimhen becoming Milan player next season will really happen considering his current deal with his club Napoli and the Napoli president saying that the player is still a player of the club Napoli even though offers has come from Saudi Arabia Which is one of the bigest deals for the player but it is not considered yet because Napoli is happy with the performance of the striker who helped them to win the league last season as the top goal scorer in SeriaA.
It would have been a huge error for Napoli to accept to any arrangement that would have allowed Osimehn to depart the club. He's their finest player right now, and he's brought them a title they haven't won in over a decade. Even if other top teams are interested in him, letting him go now will be a major risk. If Napoli allows him to leave, one can conclude that the team is only interested in financial gain and not the overall success of the club. He can depart after the next season if excellent offers come his way; by then, he would have accomplished a lot for the squad and been adequately compensated.
Osimehn joining Milan is going to be a huge deal for Napoli but I think Napoli will rather sell Osihmen to another club to make money when he still has one year contract with the club than letting him join Milan as a free agent that will be of no profit for the club but rather Milan will be a stronger opposition for Napoli to play against.
I doubt Osimehn will want to join Milan as a free agent if his contract at Napoli expires without him leaving the club by then. He's a fantastic player and striker who can score goals. If he continues to play as well as he did last season, many great offers will come for him to join them, and I'm sure Napoli will gladly accept and sell him rather than waiting for his contract to expire and leaving as a free agent, which would be a huge loss to the team.