I don't think United will be active in the January transfer window because it will be more costly to get the right players during this period. Also, most players prefer moving in the summer window, and the kind of players available in January window are fringed players with less game time at their clubs. Two areas that I think needs reinforcement are left wingback and a top striker. They've signed Diego Leon which will be available next season, so Amorim just has to make do with his crop of players till the season ends and bring whoever he wants in the summer window.
I don't agree with this. A mistake clubs make is trying to fill up the missing pieces all in one transfer window. That's not how to reinforce a team.
I believe Manchester United should make at least 2 signings in the January transfer. If the scouting team is serious, they can get very good players by January. The coach and board just need to agree on which part of the team is the most pressing and find a way to fill that part. Then by the summer, they can make more 3 or 4 signings and you'll be surprised to see that they have a very good squad.
Building a squad takes time, the manager needs to identify what is the most pressing position of the team and fix them in that order. If they continue like that for 2 years, they can have a competitive team. But I don't expect Manchester United to do that because the club itself is not in order. They still have to fix the hierarchy of the club and get the right board members and sporting directions to handle the team. I don't think the sporting directors in United have been doing a good job wen you consider the kind of players they've been employing.