Man United should be able to take advantage of Man City unstable condition. But on the other hand if they still can't beat Man City, it should be considered reasonable. Amorim is still very new and so far not many players can understand the coach's wishes. When Amorim held Sporting, he could easily silence Pep Guardiola, but now Amorim holds Man United where this club has problems that have not been resolved by any coach for a long time.
Yes, that's right. Man United should be able to take advantage of Man City's current slump, in fact Man City's current slump is very severe from the last 10 matches in all competitions Man City only won 1, drew 2, and lost 7 times. Of course this should be a motivation for Ruben Amorim's troops when facing the derby later, especially as you said, not long ago when Amorim was still coaching Sporting Lisbon he managed to beat Man City with a score of 4-1, this will indirectly increase Amorim's confidence in this match.
Moreover, in this derby match, Man United is very ambitious to win in order to boost their position in the standings. Currently, Man United is in 13th place with 19 points. Although the Manchester derby will take place at Man City's home ground, Etihad Stadium, but if Amorim takes advantage of the lack of confidence of Man City players, I think they can win this match, although Man United is also not stable but under Amorim Man United's game has improved, it's just that they need to take advantage of opportunities to score goals.