Osimhen's career has dimmed a bit after he decided to join Galatasaray but actually had no other choice but that and that made Osimhen no longer glanced at by European teams.
So indeed Osimhen's decision to join the Saudi Arabian team to get a lot of money was not the wrong decision because he did not want to take many risks for his career and preferred to get more money while there was an opportunity.
After playing in Saudi Arabia for a few seasons, he could return to Europe with his transfer certificate in hand. He may miss his prime, but he could experience Europe once again as someone who has earned more money... If you ask me, I would say this is undoubtedly a bad career planning, but life sometimes forces us to do what is rational...
By the way, I haven't seen any official announcement about Osimhen and Al Hilal, but there are reports in the media suggesting that the chances of this transfer happening are very high...