A lot depends on (a) how many combinations there are and (b) what you want to do with it.
- Making more subcategories is certainly one option, and is good if there aren't too many.
- If you want to make a distinction between the "two axes" you mention (so that you could filter on each one separately, for instance), it could be possible to make a custom field for one axis. You could make it a list field, and set up a Custom List with just the values that you want to be available to that field. You would do this at the Sense level.
- If you want to use features, you can use Inflection Features even if the property is not strictly "inflectional". The name is more specific than it should be--those features are really for grammatical information of all kinds, in contrast to "phonological features". Here's a picture of part of the Inflection Feature Catalog:
There are many built-in features available, and you can create your own. But working with these will be a little more tricky. It is possible to display them in the dictionary, and see them in the Browse view, and filter or Bulk Edit them, but there are a lot of little fiddly things about all of these operations--these paths are not as well-trodden as other ones.
Earlier you were trying to add Inflection Features to a Category. You were in the right place, and looking for the "three dots menu" was the right instinct. For me, when my window was too narrow horizontally, I couldn't see the three dots. When I stretched it to the right, then they appeared, as long as I had clicked on that field and the blue triangle was visible.
-Beth