I am sure no team is interested in bringing Onana at the same price or close to what Man United initially recruited him.
Regardless of whether Onana is still in the team or not, it is only right for Amorim to bring in another goalkeeper because last season we could see that Onana did not perform well and not only that, Amorim must also get full support from the team management to build the Man United team if they want to be better next season.
When people say Onana is not performing well, I remind them that they entire team is underperforming. How do you expect a goalkeeper to be outstanding when the defense is weak. The confidence of a goalie is a good defense. Maybe a top team might not want him due to his lack of confidence and numerous costly blunders. But I am sure that an average or low-placed club can buy him. He would have to reduce his earnings and maybe sign a short term contract.
There's truth in what you just said, but Onana is a goalkeeper that is full of mistakes, and he doesn't know how to make important saves that would help his club win matches. Even though Manchester United have a good defense, Onana would still be a big problem for Manchester United because he will still commit his blunder. If Manchester United parts ways with Onana, joining another big club won't be a problem for Onana because there's a rumor that Eric Ten Hag wants his services at Bayer Leverkusen.