I'm trying to understand how its possible for the players to look so poor and so unprofessional, and the best I can come up with is this.
I think Ten Hag has gotten himself into a complete tactical knot as time has gone on. I think this has happened for a few reasons. A small part of this may be things that are outside of his control, such as the calamitous injury crisis last year and a few entirely unexpected issues with players that he could never have foreseen, leading to him having to adapt and make sudden changes to the way we play.
Above all though, I believe (and this is guesswork) that he is a well below average communicator. I get the impression that he struggles greatly to get his ideas across in a concise and understandable way, and that it leads to widespread confusion on the pitch. In order to try and rectify the poor performances, I think he poorly issues more instructions which only amplifies the confusion, and we're in an absolute doom-spiral as a result.
My opinion is that the players are so confused and full of conflicting instructions that they become completely lost on the pitch. They have no sense of where they or their teammates should be positioned. They don't know what the triggers are, they don't know when to press and when to play out or go long. This leads to a completely disjointed team where they essentially look like they haven't been coached. I think trying to make sense of what they're supposed to be doing actually makes them look sluggish and uninterested. So much of their mental energy is focused on trying to figure out what they're supposed to be doing at any given time, and as a result the game passes them by and they look like they simply aren't bothered which, given how badly things are going, probably is now true as some kind of self-fulfilling prophecy.
I think this is impossible for Ten Hag to walk back. It's gotten too muddled and too convoluted and he is not capable of wiping the slate clean and offering any kind of clarity. I would imagine he can no longer see the wood for the trees himself.
The only solution in my opinion is to sack Ten Hag, and have someone come in who can liberate the players by telling them to forget everything they think they know. I think this would lead to a temporary but extremely sharp uptick in form. I think this is exactly what happened when Ole first came in. I personally don't think it should be Ruud, but a fresh face. I would imagine that the second phase of the process so to speak would be to then slowly instill a sustainable way of playing, after you've given the players a chance to let the fog lift.