I know a lot of people would blame Manchester United for Onana's poor performance, but I believe Onana isn't good enough to become Manchester United's goalkeeper, and that contributes greatly to Onana's poor performance at the theater of dreams.
With the number of individual errors he made in Manchester United, it is safe to say that he was the architect of his own downfall. Of course the club has some blame in it, because playing in a club that is winning games would definitely give the goalie confidence, but United struggle in nearly every game they play.
I wish Onana all the best on loan, he should keep his head down and try to improve and maybe a club in one of the top five leagues might be interested in him next summer.