FA Cup is United's only chance to lift a trophy this season and they may as well win it all since City could go all out while competing for the Premier League title. They may not have enough fit players to compete in the Finals that is scheduled to be on May 25, 2024 and that's after match week 38 if I'm not mistaken.
Can they afford to lift the FA cup trophy against Man City I think is not going to be possible for them, they didn't have what it takes to lift the FA cup trophy just check out what they played yesterday against Coventry of Championship them for almost lost to Coventry yesterday if not for Coventry player that miss their penalty, don't know that they would have lost the game yesterday so I have a strong feeling that Man City is going to won them in the final.
This is football so it's possible. I already set out the things that could happen to City before they even faced Man United for the FA Cup Finals. The competition is tight for the Premier League title so every City's player have to compete every week on a very high level. That may cause a lot of injuries to them and that's going to be advantageous to United who only have to maintain top 7.
If you look at Man United's performance when they played against Coventry yesterday, I doubt that they will be able to match Man City's game. This is like a fight between David and Goliath, where Man United performed very badly and they even seemed to be playing without a rhythm. Meanwhile, Man City, even though they have now been eliminated from the Champions League, but their performance is still very impressive. Even though Man City is playing without their first squad, I still doubt Man United can win against them.