Summarize tool field selection improvement

[Bennu]

Currently the summarize tool field selector has one empty column on the left side that must be clicked on when selecting the fields, otherwise the 'Add' button does not activate.

I don't understand why the need for this empty column to be used when selecting the fields to aggregate/calculate.  Why can't we select the fields by clicking directly on the names of the fields instead?  Selecting fields this way is actually possible, but then the 'Add' button does not allow for the selection of the 'Group by' or aggregation method.

This creates confusion, especially for beginner users who might click on the field names, see them selected and be puzzled why the 'Add' button is not working.

Thanks!