This could be the worst Premier League for Man United as they are likely to finish outside the top 10, but I agree with you that their poor (Premier League) performance is not entirely Amorim's fault, and I think he just happened to come in at the wrong time. Give him more time and full financial backing, I am sure he will make Man United better, and back to the title race.
In contrast to the Premier League, Man United is shining in the Europa League and I think they have a pretty good chance of becoming champions, especially if Amorim really prioritizes the Europa League above everything else. If this happens, then it is no surprise that Man United will lose against Nottingham Forest.
Amorim came when Manchester United was very down and it was not easy for Amorim to make changes in a short time so what is happening now is not entirely Amorim's responsibility.
Manchester United's position in the Premier League is currently very bad but I will not overreact, especially now that Manchester United has shifted its focus to the Europa League competition because there they are likely to win the title and get a ticket to the Champions League next season so that will be their priority.
For the match against Nottingham Forest this weekend I think it is quite difficult for Manchester United, especially since Nottingham Forest is in top form so I will not have high expectations for Manchester United in the next match.