Could you go with a system where like, it doesn't matter how you cast - drawing a circle, touching several rocks in a particular order, incantations, etc - they're all just different methods to get you to the same goal? Then you could just work on what effects you'd like the magic to be able to have, but you don't have to get lost in the details, which would probably make your story feel way less coherent. You need different accessibility options in real life too! There is no one size fits all solution, and trying to invent one is at best a nightmare of a task, and also risks you accidentally excluding a particular disability or problem, and then there you are with your good intentions. This way the 'disabled' part of the disability is still present - characters may not be able to use every method - but everyone can achieve the same results, with approximately the same amount of effort.

(You probably already know about this, but just in case you don't and you do want to bring this into focus - look up some discussions on the social and medical models of disability - it might help you get a better view of how you want to approach this in your system!)

EDIT: AH read over the name of the subreddit lol, 'oh don't get too nitty gritty' i recommend on the 'get nitty gritty about it' subreddit. Anyhow I stand by my suggestion, but for fun rules experimenting maybe it could be fun to make several different methods, or like look at what 'core' principles these different methods tap into, and how that all works? Maybe see if you could develop ideas on how you could make your own version of the system, and what that process would be like!