What to call a trait that has current utility but unclear evolutionary origin?
As you point out, people have sampled other terms like "aptation" but these terms are not commonly used.

In order to not imply anything about the evolutionary history, since it is unknown, I think it makes most sense to refer to these simply as traits or phenotypes (or genotype for that matter, depending on the approach you are taking). If you wish to emphasize that these traits are beneficial to the organism, it is sufficient to call them beneficial traits or use other adjectives like useful, positive, etc.