If you mean “a unique value present in attribute of entity ‘X’ “ that you objects of entity X have all the same value: no, this is not feasible.
You can bind a dropdown to an attribute of type Enumeration or Boolean.
You can bind a Reference selector to an entity’s association.
You could keep track of all the unique value, and create a helper objects in the domain model, and usw a reference selector.
To keep track you can use after commit microflow on the model.
Or when working on huge data sets OQL might give you some options. https://docs.mendix.com/refguide/oql