Embarrassed to say I went irate
Thank goodness his tutor refused to speak to you. She was in no way responsible for your DS's series of errors, and you would have been completely out of order to be angry with her. I can't believe that you thought this was appropriate - not a good model to your son who needs to learn how to manage his condition appropriately.
Your DS's errors, however, which would seem to stem from a combination of his neurological condition, and his youth & immaturity. So he's learnt something, I hope. Can you calmly help him to reflect on that? Rather than blame everyone else?
He should enquire about mitigation. The "because of COVID" excuse is just that - an excuse, but not by the university. Your DS should have taken up support offered at the start of his first year - way before we had to send students home, and lockdown. If the university has a proper record of his disability, then they can apply mitigation. But you - or preferably your DS - needs to look at exactly what happened.
You can read the regulations for his degree on his university's website. These will be published there as a public document. If your DS isn't capable of this, maybe this is where you could help him.
In my experience, a fail is something no department likes to hand to a student. Our systems are geared to give students the benefit of doubt, and to try to reward effort wherever possible.
It might be worth trying to understand how a degree is awarded. Generally the overall mark for a year will be a combination of marks from specific modules.
UK undergrads do a degree comprised of 360 credit points, 120 each year, and it's usually modularised eg 4 x 30 credit point modules, or 2 x 60, or any combination of modules that adds up to 120. Most universities will have a barrier of X number of credit points (usually 100 but it can vary), that a student must pass to progress to the next year of study.
There will be regulations about the minimum number of credit points a student must pass over the whole degree in order to graduate with an Honours degree, and also a minimum for a Pass degree (lower), and other exit points, such as a Certificate of Higher Education. And so on.
So your DS needs to look at what happened to mean that he does not progress to 2nd Year.
Did he plough a whole module? Did he simply not hand in any work for one unit/module of study? A lot of modules in a lot of universities don't rely simply on an end of term "sudden death" exam, but will have an essay, for example, worth 50% of the module mark, and a project, or an exam, or whatever. This is all published to students at the start of their studies each year for each module.
The fact that he's been given a re-sit suggests that he can still rescue his progress.
He needs to find out if he can go into 2nd Year, carrying this failed module, and re-submit the work in June 2021 (I have a couple of students doing this). BUT he needs to know that he will need to be super-organised to manage his 2nd Year studies and complete the failed/missing work at the same time.
This sounds like it will be a struggle. But he needs to sort out exactly why he has failed to progress to 2nd Year, and what he needs to do.
And what support his university offers for his disability. And then he needs to take that up. We can offer support, but students need to be mature enough to take up the help, and learn to manage their lives themselves (medication, exercises, eating properly, sleeping properly). If he doesn't do this, you are totally unreasonable to lambast his tutor or his university.