There are three major kinds of evidence that would be useful here. Most useful but least likely: email inside the company in which someone says "make sure that this doesn't select too many people with disabilities" or "it's fine that the system isn't selecting people with disabilities, carry on".
Useful and very likely: prima facie evidence that the software doesn't make necessary reasonable accomodations - a video captcha without an audio alternative, things like that.
Fairly useful and of moderate likelihood: statistical evidence that whatever the company said or did, it has the effect of unfairly rejecting applicants with disabilities.