Harry Maguire is the player who makes the most individual mistakes at Manchester United. If a goal is scored as a result of his mistake, Onana gets very angry. When we empathize, everyone feels the same. Goalkeepers hate scoring goals and conceding a goal because of a mistake can make them angry. I hope Onana can show the success of his former team under the Manchester United jersey.
If I make an analogy for food that must remain durable and healthy to eat, then we must be able to keep the food from being poisoned in the slightest. Likewise with a team or club that is basically very good with a line of good players like Manchester United, because even one of them has a less good player like Harry Maguire, it will destroy the whole team so that the potential of other players seems useless because it is no longer visible in the game.
Onana was just angry at the mistakes made by Harry Maguire, that's all and I think it's very natural for Onana to be angry because when there is a goal conceded that he is guarding, it will make him look like he has no skills in keeping the goal, even though the goal was conceded by defenders who do not have the skills to defend against their opponent's attacks.