For every filter configured you find the sort field, where you can select if you want to sort by item count (which is the default) or alphabetically ascending or descending. If you choose alphabetically you get another selection for the field value on which to sort alphabetically. Sorting by item count does not offer a sort field because the order is based on the number of items returned by that filter. That means that the filter which finds the most items is at the top.
Sorting is supported on text values from text fields and tagboxes, DateTime, Checkboxes, and Numbers.
For Tagboxes, which are created based on _refId the Name Pattern is shown in the Filters. Picturepark sorts tagboxes values also on the Name Pattern which must be set to “available in filters” for the field on the Layer.