FA Cup become the only one opportunity left for Manchester United winning the trophy after gap many points in Premier League and I don't sure Erik ten Hag have enough compete to make miracle for domestic league winner. In Fa Cup 5th round, Manchester United has away match for facing Nottingham Forest, Erik ten Hag have to forget last match losses against Fulham and keep trying to win the left opportunity for getting trophy in this season.
Nottingham Forest performance still not consistent yet after losing last match in Premier League against Aston Villa and other side their position standings in domestic league left fewest points with relegation zone and likely FA Cup match against Manchester United will use their second players composition.
Yes, it is true that the FA Cup is the last and only choice for Manchester United to have the opportunity to win a trophy this season. So Ten Hag will definitely take advantage of this opportunity to get maximum results. Although basically Manchester United's chances of winning the FA Cup are not big if you look at their current performance. The reason is that in the last 8 of the FA Cup there is Liverpool, who are currently at the top of the Premier League standings. So if Manchester manages to reach the final or the FA Cup final, it is very likely that Manchester United will be defeated by Liverpool. Because I believe Liverpool can most likely qualify for the FA Cup final.
Then for the Manchester United match which will face Nottingham in this big round, Manchester United will most likely win. Because as you said, Nottingham is currently in danger of being relegated from the first division of the English league. So it is certain that the focus of the Nottingham players will definitely be divided into two and this will definitely result in Nottingham's performance in the match against Manchester United being less than optimal. So Manchester United has a very big chance of advancing to the semifinals of the FA Cup.
So the point is that in the match against Nottingham, Manchester United must be able to remember the playing style of the Nottingham players. Because in the previous match in the English league, Manchester United got a little insight when they lost to Nottingham. So in this match Manchester United should be able to win the match easily.