Onana has been with Man Utd for more than 2 seasons and should have realized that he is not a good fit for Man Utd. To save his career, going elsewhere is a way out, but who wants it? There is no one because Man Utd wants a high price, or another way is to ask him to be loaned out because of course with the arrival of a new goalkeeper and currently Amorim trusts Bayindir more, so Onana is only the third choice. I really feel that Onana's career will really stagnate if he stays at Man Utd for too long.
Him staying at Manchester United can make him some money because he's still going to be paid despite him not playing. No clubs or not many will be that interested in him because he now has a bad record that not many clubs will what to associate with him. Conceding goals spoils the goalkeeper record but Onana leaving is going to be the best move for him because if he stays at Manchester united for too long, it can make him to lose form more than he currently is because he won't be playing. Getting a move out of the club in January should be his next target and not allowing the career he should have had to go to waste.