Within the Data Engineering Pane, it would be great if the duplicate/unique field had enhanced functionality to either select the duplicates (as you can select other values of interest in the other fields) or to encode a value of 0/1 to identify a duplicate entry through the creation of a new field.
Encode field is less useful for this task as it creates a field per unique entry; instead, there could be a binary option (0 == unique, 1 == duplicate).
Examples of similar workflows: