I stumbled upon this thread last night while looking for a similar solution. I found something that worked after tons of trial, error, and googling. Here's a screenshot.
It takes the array of results returned in step B, looks for the one with the highest attribute for the field called "specificity_score" and returns that RID to a field in the action step. It's not exactly sorting results but if you were looking for the "earliest" record, you could set the attribute to a "created_date" or similar, and use a min() filter instead of max()
ex:
{% set desiredrecord = b|min(attribute="created_date")%}
{{desiredrecord.desired_field}}
