Setting column names in Direct Database Query dynamically

I'm trying to set the columns I want to retrieve in the SELECT statement via an argument but keep getting this response

This query works perfectly if the fields are defined directly in the select statement. Just not if they are passed as text through to the query. And I get the same issue even if I put the column name text directly into the argument input.

WHERE, LIMIT, etc all work correctly.

Here's my setup for context.

Is this a bug or am I doing something incorrectly?