It is difficult to find a reason as to why Rashford has completely lost his best form this season. Last season Rashford impressed with 17 goals in 35 matches, while this season he has only scored 4 goals and 2 assists in 20 appearances. This is hard to believe even though Ten Hag has repeatedly given him the opportunity to prove his worth this season.
I agree that it has been a bad season for Rashford and some of the other players. Antony hasn't recorded anything in 17 appearances, Rasmus Højlund has also not lived up to expectations. Alejandro Garnacho is better than Antony, also Bruno Fernandes has a decline in his performance. This is a different season for Manchester United compared to last season, so overall their performance has really suffered.
I see Rashford's decline in performance also because he doesn't have a clear vision and mission this season. Moreover, Rasmus Højlund is still performing below expectations. The two of them still haven't found a good playing rhythm. I often see moments where Rashford makes bad decisions and seems to play alone. But overall all MU players have performed poorly this season. They are not like last season where they were able to appear as a fairly strong team in the league. This season they have really performed poorly with a goal difference of only 5 goals. I don't think they will get a place in any international matches next season.