Hi,
Unfortunately that is not available for product categories/taxonomies, at least not yet. For taxonomy terms I would recommend using a different custom field, a simple text input, or text area, not coupled with other fields.
The configuration can remain as it is, only make sure that the primary and secondary keyword logic is set as following: https://i.imgur.com/0jEnvGe.png
The mixed results ordering can be set under the ordering panel, in your case you want it like this: https://i.imgur.com/Q7YX6Tq.png
