You were there for 2 months, including a holiday. Claiming you didn't have time to book an appointment with an optician in that time will get you nowhere. Even if we only look at the working time, claiming you didn't have time to use the zoom facility on a Mac (which gives you up to 40x standard size) won't wash. If you are unfamiliar with a Mac you have to search the internet to find out how to do it, but it would only take a minute or two.
A reasonable adjustment is something that removes or reduces a disadvantage related to your disability when doing your job. As far as I can see, extending probation is a red herring. I cannot see how it helps. Changing the tone of feedback is also unlikely to fly as a reasonable adjustment.
A larger screen may be a reasonable adjustment, but if the zoom feature on the Mac wasn't enough, a larger screen is unlikely to be the answer.
If you go to tribunal with a story as muddled as the one you have presented here, you will get nowhere. Even if you get your story straight, your employer's version will be very different. They will talk about an employee who was failing to meet the required standard, who had been given plenty of feedback over 2 months but still wasn't good enough and who then, when she knew she was likely to be dismissed, tried to use disability as a get out of jail free card. I'm not saying that is how it was, but it wouldn't surprise me if that or something close to it was your employer's version of events.
You may have legal cover on your house insurance. If so, you may be able to get them to pay for you to consult an employment lawyer. But that should be your next step. They will be able to advise if you have a case worth taking to tribunal.