Select/unselect all subforums inside a Category in Fluid View

Currently, when we click the Category heading in the filters widget, all the checkboxes/subforums under the category get selected (toggle behavior).

However, there is no way the user would know that is how it works and they select/unselect each subforum manually which is a bad UX.

Instead, there should be a checkbox for each Category heading too which will bulk-toggle the selections of all subforums under the category (expected behavior).

TIA