I think that CR7 left mainly because of the treatment by MU and because of how Ten Hag wanted to have him on the bench, for that reason I have always said that Ten Hag is not good as a coach and that I hope he has changed, however for me Ten Hag was an unstoppable destroyer of clubs, of players and then finished alone without important trophies, now with the new opportunity of Leverkusen I hope he redeems himself, with the Saudi League I think that if CR7 returns it could be for Al Hilal to compete in the Club World Cup.
Ronaldo left the club by many reasons but most important, in my opinion, is their disrespect on him. They believed in Ten Hag and wanted to kick Cristiano Ronaldo out of the club in very disrespectful way. Therefore, Cristiano Ronaldo with his high ego, felt not only uncomfortable but very disappointed and he overreacted with this. I dislike the way he hosted an interview and revealed many negative things in the club, of course I am not naive to believe all things he said are true.
Some years later, Manchester United have fallen into a even worse crisis than when they had in very last months with appearance of Cristiano Ronaldo at their club. It's logical and evidence-based enough to say their blame on Ronaldo seasons ago was completely wrong.