> I've never been the kind of A type personality ...
That's a poor way of characterizing the issue. I think you should look more closely at why you haven't done well instead of internalizing that you are just not the right type of personality.
> I've been told I have ADHD
A lot of heavy metal poisoning is often mistaken or misdiagnosed for spectrum disorders. Its hard to test for chronic poisoning because you have to take a chelator which causes acute poisoning to even test for it. Having been labelled in this category often is a disadvantage because structure is incredibly important for people on the spectrum but you can ask for certain accommodations and they are required to give them if you have a diagnosis.
> told I won't be receiving a CS degree ... because my grades weren't good enough for entry.
You have not said where you are located, but if its anywhere in the US this is par for the course. Its important to recognize the reasons for the failures and place blame where it actually belongs.
Many times in US based curricula, the student is set up to fail, and by that I mean in any other industry if the same practices were followed it would be fraud and they'd be found liable. That being said, sometimes it is because you have repeated personal failures and not addressed them, but this latter aspect is in the minority.
What I'd suggest is re-examining your failures, and identify exactly what caused them with a objective view, and what if anything you can do to fix them.
Start with examining what any student needs to control basic academic outcomes, and whether those requirements were met for the classes you took.
When setting up your schedule, were the classes appropriately advertised based on the amount of time they require for pass. Classes are rated by unit hours, if the college recognizes a 12-unit course as a full load, divide 40 hours by 12 and you've got the max number of hours any class should require (per week per unit) in coursework for the 16 or 12 week period. You cannot expect your best work if one or multiple classes exceed this since you'd be exceeding safe limits for any professional job. No one does well when something requires 60+ hours of work a week for an extended period of time. This can actually send people to the hospital. If its above 40, they have not provided the necessary control over basic academic outcomes.
Additionally, structure of the course is important. There are systems properties
that are necessary for any test/exam to be valid, or have a valid inferential basis; these properties are normally covered in an EE class; take an overview look at the properties from MIT OCWs videos. You may need to look at the book but its cheap and well worth having. Don't worry about the math, look at what the properties are, how they are defined and tested.
The professor may have removed or added properties (without understanding this rigorous approach) to limit the people who pass, or fail people. They may do this for any arbitrary reason.
This is often seen in non-deterministic questions being asked on tests without a basis for inference. An example might be a multiple choice question with 3 or more actually correct answers to choose from (breaks determinism and inference).
Causality spirals are specifically designed to fail people. An example of these is the classic 3 question test which I've seen numerous times in engineering tracks, where the 2nd question requires the correct answer from the 1st question, and the 3rd question requires the correct answer to the second question. Classes that use these often have two main tests, which don't occur until you can no longer receive a refund.
Ultimately they amount to the whole grade, and you can only get 1 question wrong out of the two last question on either test and still pass.
Additionally, there may be other dirty tactics that further optimize for failure. An online grader may randomize each individual students question pool. If there is a problem with the questions, the professor may not take action for a question that other students didn't get, there is no clear signal to them that something is wrong with the test and they didn't vet the question pool.
Online material and graders may mark correct answers as incorrect, and have subtle dark patterns embedded to induce failure spirals. They may not provide a means to report problems to the professor. This is done by not providing a button, and the dark patterns may have text on a red background that pops up with each incorrect answer after every question. Its the opposite pattern for dopamine loops which are embedded into games as addiction triggers, only this is a frustration trigger. It does this when the question was answered correctly, you get no popup when its correct, you get a red popup when its incorrect. Its subtle, but after 4 or 5 times of this happening, you can't concentrate because its futile, and that applies to a broad set of the population. Its known pedagogical circles that this causes poor outcomes, there was a classic psychology experiment where this was tested by telling the teacher a particular low performing student was gifted, and the low performing students did better when they were told that compared to when they were told they were low performing.
Mismatched coursework, inference requires matched coursework; if the lecture and material covered do not match what's tested, they are testing your guessing or mindreading ability. This is common in courses that pay professors to teach who then refer their students to Khan Academy (yes this happens regularly), and online material such as an etextbook where the reading doesn't match what is being tested.
Lack of any redemption mechanisms so snowballs continue until dropout.
This usually means no extra credit, no test retakes, no communication regarding the exact material that will be tested, no study guides that are verified for accuracy before the test, and no legitimate guidance provided by the professor during office hours. These all happen regularly in academia and impact outcomes towards the negative.
There is an escalation path if these issues are the case, but unfortunately unless you know how to accurately document and case-build, and have the money for a lawyer to sue them; by the time you get to reaching out to the Board of Trustees, you may still get no action.
After all, all bureaucracy seeks a lowest common denominator, which is often negative production value; and in any bureaucratic system standing is important and the people in these positions have their standing threatened since they themselves are also teachers or were at one point. Its easier for them to do nothing, since taking any action against their peers threatens their social standing among educators, they are all in it together first, and for the student second. These are longstanding issues that are common with any centralized structure that lead to corrupt systems.
There is a rule of thumb for checking disadvantaged structure based off probability, but it requires multivariable calculus and really doesn't tell you much except that you need to dig in more detail.
Probabilities are also notoriously impractical when it comes to actual likelihoods, its useful in finding out whether the distribution curve for passing has been scrunched to the point of pass|fail with extremely narrow outcomes.
Most of these problems are found in core transfer classes that are always full. The result is people can't transfer into specific programs since they often can't pass those gatekeeping courses with arbitrary pass requirements.
Some courses structured as described have a pass rate of less than 10%, and that includes all previous years of dropouts among the pool of potential passes; they don't track re-attempts.
The people that pass these courses are often people who break academic honesty policies. I won't tell you to do that, but sometimes in a corrupt/fraudulent system where they've lied or misled about the actual prospect of completion, I can't say its not a reasonable alternative given the lack of any kind of reform possible and the lack of any actual due process within the system. Being state funded means that often, absent any gross provable negligence, nothing legal will have standing; but you'd need to talk to a lawyer (with a proper case built, either for discrimination or fraud). If you plan to go the latter route, I'd suggest not tipping your hand.
Also, I've run into a few instances where test questions have marked my answer as incorrect when it was correct, and upon review it showed the answer they claimed I submitted was not the answer I submitted. I would suggest you use a screen recorder while you are doing any kind of assignment like this since you cannot trust anything will be above board.