pfa attached . was trying a few things and got to this . i am able to get the number of count the filter has changed. of course there are some limitation. you will find out once you open the qvw. If possible please build something on top of it and try out something similar to help the OP. I am familiar with Qlikview so tried it in Qlikview. With all of yours help i guess we can easily replicate the final document to Sense.
One thing strange I am noticing is that if I select SubCategory, nothing happens (which is good), but when I clear SubCategory, the count increases by 1. I wonder how is unselecting SubCategory related to On Select on Category. I would have thought that they are unrelated, but seems like they are not which is a problem.
I am sure there is ought to be a Qlik Sense extension which allows you to have triggers, but I am just not the right guy to know about it.... may be someone else can help here