My Customizing Filters for Better Accessibility post from July 2020 talked about how to simplify filters so that they work better for keyboard-only and screen reader users. One thing I didn't realize at the time is that including the "All" value in a list or dropdown list filter (or set control) makes them behave poorly with screen readers. The reason is that the "All" value turns the filter into a widget that is unlike a standard ARIA combobox or listbox that assistive technologies understand. The state of the "All" value controls the states of all of the other values in the filter. That's really powerful to be sure, but it's unique to Tableau and not well understood by assistive technologies like screen readers.
For the best behavior with screen readers, you should disable the "All" value for any list and dropdown list filters (or set controls) in dashboards you're trying to make as accessible as possible.
