Even though you say Man United won against weak teams in the league, I see many changes made by Man United and this is an important asset to face Copenhagen and in the next match Man United will face Man City.
Man United's victory over Sheffield United saw a lot of changes made by Man United players, especially Onana, in that match, he performed very well, making many crucial saves which saved Man United's goal from being conceded, Maguire was also starting to get better, he was even the MVP in that match. .
So I think Man United against Copenhagen, this match will be won by Man United, especially since this match will be played at home, of course this will be a special motivation to play in front of your own fans. I'm sure that Man United's downturn will slowly heal. Apart from wanting to secure second place in the group, in the UCL match, they also want this victory to raise their self-confidence before facing Man City next week.