I also agree with you that Onana needs a new environment because it's clear as day that Man UTD don't hold him in high regard anymore. It now looks as if he is an average goalkeeper whereas he was undoubtedly the best goalkeeper you could have. When he was at Ajax, he was fire, at Inter Milan, you can't dare him but as he moved to England, his form and confidence dropped. I feel that he'd be appreciated somewhere else more than he is now at Man UTD.
Andre Onana is just under pressure, this one of the reasons he's not exploring and succeeding in Old Trafford. When he was in his previous clubs, nobody expected much from him because there have been divided attention to the players because the goalie is only present to do his best keeping saves but in Old Trafford, they expects every goalie to be at their best, besides he was fulfilling the shoes of David De Gea who everyone thought to be 3x times better but it reverse is the case.
Manchester United will struggle this season base on the unpredictable rigid foundation of Ruben Amorim. How can a manager have competent players and new signings and still been unable to accomplish top results.