Winning the Champions League is not a one Man Job. Ronaldo moving in another Club doesn't guarantee he'll win the Champions League. As it might be another season with Juventus a wasted one hope's of winning the Champions League got all shattered in shambles. Further more, he should stay put at Manchester United.
you are right It is impossible to win a title on a platform like the Champions League depending on the performance of just one player. Doing well in the Champions League definitely requires good teamwork and good strategy. And so Ronaldo should now try to make the United team more stable with Manchester United. United will be in contention for the Champions League title in the 2023-24 season if the squad is stable.
No matter how great a player is, if his team is not in a good condition, it certainly won't make the team champion. Teamwork and good gameplay are one of the factors for a team to become a champion. I myself have no doubts about Ronaldo's ability, but with the current state of his team I cannot comment on Ronaldo's performance.