Man United is facing a complicated situation, and I think Ruben Amorim must have known what their problem was and maybe he also knows what the solution should be, but unfortunately he can't do much because without money and no players sold in the transfer market, then he can only rely on existing resources, and that is not a solution.
The worst is their striker. Either because they are not suited to the new strategy or their abilities are limited to that, but what is clear neither of them could really make a meaningful contribution. That problem hasn't been resolved yet, and now a new problem has emerged as Lisandro Martinez has a long injury.
Indeed, Man United's problems are very complete, it is very difficult to make Man United rise or at least be consistent like in the European league. Apart from the fact that they need a lot of additional players, I think this is also Amorim's fault, he knows Man United's problems but he doesn't seem to want to change. Using 4 defenders is difficult, let alone 3 defenders. Amorim is not sensitive to forcing the philosophy of 3 defenders. Too many players are injured, they also can't duel in the air, so it seems that Amorim continues to experiment every time he plays.
If he was good at tactics, he wouldn't have maintained the 343 formation with the same mistake as Ten Hag. In the Sir Alex era, many formations and player formations were tried when many of their players were injured, there was always a solution, Man United was always identical to the 442 formation. In addition, Amorim should have played Onana, he is not good, he often passes forward incorrectly even though he can control the ball, and for Maino he is very good at the front but doesn't get a place from the middle even though he is good at helping to the middle. Amorim must realize this so that he can be better in the next match, and of course this is also for the sake of his career so that he doesn't get fired.