Serie A clubs are actually clubs that are always able to utilize players who are considered ordinary at first to become extraordinary in the end. So in fact, when Inter Milan last season made it to the UCL final, we all knew that at that time the squad depth of the two teams was very different in terms of quality. but what happened was that Inter Milan could indeed match Man City very well. And yes, the 1 goal scored in the final match is also proof that Man City also couldn't do much against Inter Milan, who at that time still relied on Onana. Onana was a great goalkeeper at Inter Milan. but when Onana went to Man United we saw that Onana was a goalkeeper who was not that good. Well, this is what I mean, the Inter Milan teams always succeed in utilizing their players to their maximum limits. And I am also quite sure that despite all their limitations, the Italian teams will one day succeed in lifting the UCL trophy again.
It has been a long time ago if the series A is famous for a big league that can always create new talents with extraordinary talent and if we remember again there are so many legendary players who used to have very high quality talent so it is no wonder that the team from series A is always successful or almost almost won the title in a prestigious competition like Inter Milan that you said and on the one hand there is also a representative of the A series (Atalanta) who successfully defeated Leverkusen who is famous for the performance is very consistent without defeating but the fact is Atalanta with an appearance that is not so good but can get rid of Leverkusen.
Inter Milan at that time could almost get an UCL title if he could hold the match draw and ended with the penalty of Inter opportunities to be bigger but even though it failed was one of the proofs that Inter was actually one of the strongest teams at UCL after Man City.
but related to the onana that you say when with Inter looks very strong but when in Man United his appearance looks bad and that's actually if you explore what is happening with Onana at this time is not his mistake but a different defense has Inter and Man United.
without I have to explain again you might be able to see how Man United defense with Inter is far different and goalkeepers like Onana when with Inter have great support from Inter defense that always helps secure the goal but when you are in Man United, are you seeing you great support from Man United defense?
one evidence if Onana is still a good goalkeeper when he was at UCL and at that time Onana managed to secure his goal from a penalty kick.