Manchester United's problem is not the number of players they sign (or that they need to sign), because they always buy a lot of players but those players are often overpaid and there is no logic behind. They bought Højlund, they paid like 70-80 million euros for a player who was not even a regular in Atalanta's line up and scored just a few goals, why would you do that? And why would you get Casemiro at the end of his carrier, giving a bunch of money to Real Madrid? Again, they are just buying random players without any plan behind.
You'll hear enough ideas from people in the situation of Man U, I mean people who do not even have any idea at all, but are using the lowly situation to say as if they know better. Well, in your case, I agree that it's not about the lack of players or spending money on them, Man U does that, but still, no good result.
However, I disagree with you about wasting money on unqualified players. Qualified or not, Man U needs to break the jinx following it and overhaul the mindset of its entire squad. Bringing more players into the same mindset will yield no good result.
This Manchester united team is just in serious lack of quality for them to return back to the Manchester united of old, and for them to get to that level they must spend heavily just as every other top teams do out there.
A few days ago I think Jose Mourinho was ask if onana was part of the major reason Manchester united were struggling last season, he said no, that why Manchester united are struggling is because they lack a quality attacker that can guarantees them 20 goals or more a season, that a team needs goals to strive, which Manchester united isn't getting easily, so in my own opinion I think he is right, this Manchester united team lack goals, and if you watch very well, since sir Alex Ferguson left the club they have not gotten a striker that can deliver the least 15 goals a season, so if they can fix that, I believe that they can be great again in no distance time if they can do that very soon .