Professional football is complicated. When a coach leaves a team, the new coach who comes in makes changes that some players don't like, and they decide to leave the team even if it means going to a lower-ranked team. This was the case with Mitrovic.

Mitrovic Leaves Al Hilal, Set to Join Al Rayyan on Huge Deal
https://onefootball.com/en/news/mitrovic-leaves-al-hilal-set-to-join-al-rayyan-on-huge-deal-41613542Last season, coach Jorge Jesus, when he was still coach of Al Hilal, commented on Mitrovic's situation. I remember that in that interview, Jorge Jesus said that Mitrovic had fitness problems and talked about his injuries. But from what I understood in the interview, Jorge Jesus was not optimistic about his future. I see that Simone Inzaghi also realized the same thing, which is why he rushed to sign Darwin Nunez.
I think if he really does receive a good offer from Al Rayyan, he would be better off moving there. Nunez will certainly replace him, as he's currently injured, which will undoubtedly push him further down the pecking order at Al Hilal. Furthermore, his contract with Al Hilal only has one season left. So, given that, I think as long as a team offers him a high-priced contract, I don't think Mitrovic should pass it up. Given his current situation, I doubt he'll get another contract extension at Al Hilal. With that in mind, I think Mitrovic might not receive a good offer like this next season. With that in mind, I think he should take it. At the age of 30, I think he should consider finding a team that can offer him a long-term contract with a high salary. Because I'm sure that even if he returns to Europe, he won't have much hope there anymore.