The defeat from Bournemouth has shown that currently Manchester United has many weaknesses that they must immediately improve, actually in the match against Manchester City they have shown a good and solid game between lines, but we don't see that when they play against Bournemouth, in addition to consistency, it seems that defense is still the reason why it is easy for the opposing team to scoring in Onana goal, so maybe now Amorim needs to find a right line up Especially in their defense, the transfer market may be an alternative for Amorim to improve his squad, but with the amount of money they has spent previously, that it will not have an impact on their finances if they sign players again in january?
The amount they had spent just on transfers last summer

What are the major weaknesses of the Red devils? The defendlines and attack role are not effective as it should be and creating awareness of insufficient force to drive through oppositions. All elite team have weakness this season and we're not just going to talk about Manchester United but also Manchester City. It becomes open to see both Manchester clubs suffering streak defeats and that's no clear chance for growth for these teams. Pep Guardiola and Ruben Amorim are still working on producing more intriguing outcome for their perspectives sides. Why blame Ruben Amorim for the humiliating defeat against Bournemouth this past weekend? They conceded 3 goals and its all coincidence? Ofcourse not because the Cherries was fully prepared and executed forceful strategy that lure their oppositions to give room for defeats.
Bournemouth performed very well and was able to take advantage of every weakness of Manchester United with the right strategy, I admit that against the red devils squad, Bournemouth was better prepared than Manchester United, but surely you know that the English league is a very competitive league, so the team that is not ready will certainly get the consequences (defeat) in a match, so I think it's not a good reason for us to say as the cause of the bad results achieved by Manchester in the match.
Indeed, no team is perfect today even the big teams in the English league have weakness, the two Manchester teams are indeed in a slump at the moment and they have weaknesses that can be exploited by every opponent to win over them, but compared from manchester city, I actually see that manchester united has the worst problem, manchester city has a bad defence after losing Rodri but they still have an impressive and sharp attacking line in my opinion, while manchester united precisely they have many weaknesses in every line.