Why sound like Onana was the only issue at Manchester United, that's not true because the cause it's a team problem involving both the management. It's normal for any player who leaves Manchester United to do better elsewhere, Onana leaving Manchester United is a redemption to himself and to his career. Manchester United has spoken less of Onana like he is the only issue, now he is out let's see how quickly they will evaluate the whole issue and sort out their crisis.
Of course other players also made mistake, but the mistake done by Onana was too obvious.
He was one of the reason why Manchester United didn't win against Grimsby Town, he made an error that lead to goal. The new goalkeeper e.g. Lammens, I don't expect too much, as same as Bayindir.
Probably we will see Manchester United's goalkeeper is still bad, but less making error.