@Cliff1975, I'm so sorry to hear what's been happening with your DS. The fact that he's lied to you suggests strongly that he's very worried, upset and ashamed at not coping and I agree with others that say dial down your natural anger. He needs all the sympathy and understanding you can give him right now.
Cambridge may not be the best fit for him, even if he's obviously clever enough because the relentless workload is really different from other universities. Somewhere else, he might have only one essay/ piece of work a term rather than 1 to 2 per week and then be able to manage (I can't actually remember if he's arts and humanities and has essays?).
The most important thing is not whether or not he stays at Cambridge, takes time out and returns or takes the rest of this year off and goes somewhere else (I think Cambridge will help with the process of going somewhere else if this is best for him). The most important thing is that he still feels you're on his side no matter what and you completely understand and accept that he's struggled and then felt too afraid not to lie about this. He needs to know, feel and believe that whatever happens next, you'll always back him and never let him feel ashamed if Cambridge just didn't work out for him.
Meanwhile, you probably need to deal with your own feelings about what's happened, somewhere out of earshot from him. He just needs to feel your love. Ultimately, it really doesn't matter if he completes his degree at Cambridge or anywhere else. What matters most is his self-esteem. He and you already know he's got the brains to do well but he needs to figure out the best way of harnessing his intellect so he can achieve any goals he wants. If he has ADHD, he'll find it massively difficult to manage multi-tasking the Cambridge workload.
I guess the starting point is to focus on the fact that he did submit two essays this term. That's great. How did he do this? What helped? What's gone wrong and how? How can you help him to feel he doesn't need to lie to you?
Very good luck with your Zoom session with his tutor. The fact that he didn't go to the meeting with his DOS and senior tutor last week strongly suggests he's just too afraid even if, superficially, this might come across as not caring or bravado. I'm so sorry once again that this is happening.