I have been doing ADA compliance professionally for a while. There is no magic on this one. There's no existing solution that doesn't require manual interference because it requires context. Human context. It has to be understood to be understandable. There's a few things you can do to improve overall accessibility but nothing in a suite. I specialize in InDesign and it's probably the most powerful document solution going. But it requires a lot of work to meet the most basic of requirements.

I’m dealing with this right now too.

My advise is to ditch the PDFs where possible, and go with HTML documents. They are far easier to make accessible. The down side is you can’t easily pass them around in a self contained way that isn’t a bit wonky compared to a PDF or DOCX. But if you just link to them in a course, or otherwise expect students to just access them in a browser, HTML pages can work well.

PDFs have always been a nightmare, and the new accessibility rules are making thousands of people in education finally realize that.

If you're in the US, your university already has an accessibility office, and they probably have at least advice and at best some fancy expensive software that does what you want.

Other countries might have the same. If not, you can try just using screen readers and such, though I don't have any recommendations myself.

Although it may not be ideal for a large document, I have used the Coblis for individual figures that I'm worried about. I usually find small tweaks to the colors can make them much more readily differentiable in the simulator.