I'm sure there won't be much United can get in the winter transfer market. He'll get rid of some and bring in some. Although Amorim may have a list of players he wants. Not all of them will be available to United.
As you said, Amorim may have to get a new goalkeeper too. Who of course has better qualities. Onana has made many mistakes since Ten Hag's season in charge. I'm sure Amorim will have to think about getting a better replacement.
It would be more ideal for Amorim to do it in the summer window to recruit the players he wants, so what he is currently doing is just to maximize the available players and evaluate them at the same time. So, we agree that Man United will not do it in this winter window. However, it seems that some United players will be removed by Amorim, even now several players are being rumored. For the goalkeeper, Amorim could look for a replacement for Onana. Or, he will keep him. Because, the system that Amorim implements requires a typical goalkeeper figure like Onana. More precisely, Amorim has the same system of starting to build attacks starting from the defense area. However, if Onana's performance cannot be improved, it is likely that Amorim will also kick him out. I am curious, will Amorim make a major overhaul of his squad later. This is interesting after, whether United will improve much under Amorim's guidance.
If Amorim were to keep Onana, I believe United's focus for the winter transfer window would be more on attack and defense. Because it seems that those are the areas that United are having problems with.
If Amorim wanted to make a major overhaul of his squad, that could happen, but as you said, the ideal time would probably be in the summer. Amorim could get a few in this winter would be great. And that would mean there would be a few names that United is ready to let go as rumored.
If Amorim keeps the current squad, I'm not sure United would get a good result either.
I don't think it's a rumor that Manchester United wants to offload some player because everyone wants success for the club. Amorim has made his first signing of 17 years old fullback Diego Leon from Cerro Porteno for 3 million pounds. He will start playing for Manchester United in July 2025. Which means that we will see more of him next season. This season is for Amorim to do his selections of players to leave the club ,and bring in replacements that will fit into his game pattern.