Certainly, Ten Hag must bear the main responsibility for Mu's decline, setting aside the sideline issues regarding the club's ownership changes. Ten Hag has had ample time and funds for squad building. Mu's current struggles mostly stem from instability in the locker room, and Ten Hag is at the center of it all. Strict discipline is necessary, but it should be applied fairly, not favoring certain players to avoid unwarranted tensions.
Additionally, Ten Hag's tactics this season need scrutiny. He consistently makes errors in substitutions and unwarranted changes in playstyle, leading Mu to relinquish leads in matches where they had the upper hand, notably in the UCL group stage against Galatasaray and Copenhagen. After those defeats, instead of taking responsibility as a coach, he often blames his players or attributes it to the opponent's strength. It's a concerning pattern that raises questions about his leadership and decision-making, factors crucial to Mu's performance.
but what I know at the moment is that Ten Hag bad attitude is related to players having a lot of injuries, so he is very confused about making Man United appear stronger, while many players are injured, so he often changes players. but this doesn't mean I'm defending Ten Hag, it's just that all this badness has a cause, but it's still the responsibility of a coach to maintain his performance even though many players are injured no matter what and Ten Hag should be more grateful to be in team that has fairly stable finances and he should also looking at the example of teams from La Liga like Barcelona still performing perfectly even though the only players they get are free players, while Ten Hag can appoint anyone he wants to recruit and Ten Hag has to look for problem spots, why many players have rejected offers from Man United several times at that time. and in my opinion, some players rejected Man United offer, perhaps because Ten Hag was less professional or had a character that the players didn't like, so other players who knew were hesitant to join Man United.
I slightly think that it seems like Ten Hag will be retained at Man United until the end of season and if he still can't get the best ranking in the standings he will definitely be fired from his position soon.