There's alot to handle in Old Trafford, Erik Ten Hag working on that and hopes to fixed these issues in immediate time given. Manchester United will improved with time, the coach have the best players to handle, all what they needs is just time to progress and adapt. Erik Ten Hag made the right decision when he signed Andre Onana from Inter Milan. He's the first choice of united and have made both crucial saves and blunders in league games, perhaps the Red Devils are having challenging moments and weaknesses are open to their opponents.
It's true, there are still many things that Ten Hag needs to improve at Old Trafford this season. The team performance has not been completely stable, a storm of injuries has plagued the players, and this is coupled with allegations of violence committed by Antony. A situation where Ten Hag is really being tested so he can get out of pressure, and the match against Brighton this weekend could be a moment for United's revival at home.
Overall, the addition of several new players to the Man United squad this season is quite good, not just Onana. Mason Mount, Sofyan Amrabat, Hojlund are considered to be able to boost the Red Devils performance. Of course, as you mentioned, things take a little time to get better.