I remember some people were comparing De Gea and Onana which showed us that Onana had a better performance in Serie A however I think the situation in these two leagues is not the same and Onana had a good performance there is a chance to have a weaker performance in Premier League because I saw Premier League for more and better strikers and more goals in the games while in Serie A the playing style is not the same with Premier League.
We can't judge Onana's performance at the moment because he plays for Manchester United in the Premier League In the new season, we can not judge whether Onana can be better than De Gea or not.
But from several pre-season matches, Onana actually did appear so bad not and he seems to be able to provide a competitive game for Manchester United in the future.
If you say that Onana's game in Serie A is clearly very different, considering that the Premier League is filled with big, strong clubs with attacking players for each club, it is very sharp.