Exactly. De Gea was way younger when he transferred to United from Atletico to replace the legendary Edwin van der Sar. You can't use the lack of experience excuse on Onana either since he got enough already for professional footballers's standard so his mistakes is mostly due to his poor decision making and overall skills as a goalkeeper.
Manchester united will suffer major setbacks this new season, it's just a matter of time before everything stand appropriate for the club. The new goalkeeper, Andre Onana been criticized by fans for his poor performance in friendly games. The Cameroonian have good footings on the ball and always outside his box, so conceding far away shots would be achievable by his opponents. United former goalkeeper, David de Gea had his own blunders, but he still made good performance at Old Trafford. Then look at the Andre Onana, already opening his weaknesses and the league haven't started, let's see how everything will plan out.