Ok, so for me Category is a taxonomy for the Event select which is a CPT. So what I did for this was using the PHP filter acf/load_field I populate the choices with all events this way I at least get the value onto the page. Then on the JS side I use acf.add_action('load_field/key=..., func) to find the parent Category and filter the choices there.
This seems like a lot for what I’m trying to do but I couldn’t figure out a better way. Let me know if I’m missing something obvious.