I’ve seen many fans and pundits make this claim. Do you think Manchester United players aren’t playing as well as they can in hope to get Ten Hag sacked. I’ve seen this argument used against Rashford as people since he’s got his new contract he’s just content to get his money and play as well.
Though Hoijund has claimed the players all back Ten Hag still https://www.theguardian.com/football/2023/nov/09/erik-ten-hag-manchester-united-squad-backing-rasmus-hojlund
A lot of punditry comes down to really simplistic generalisations like players aren’t trying hard enough because the actual reasons for bad performance are difficult to analyse or sometimes just due to the high variance of football as a sport. Reading between the lines it doesn’t seem like Ten Hag is great at motivating that particular squad but I doubt players are consciously half arsing it.