It looks like
TurboTax programming correctly reflects the current law.
According to the
instructions for Schedule
IN-529: Indiana’s College Choice 529 Education Savings Plan Credit,
"This credit … is available to an individual filing a single return or to
a married couple filing a joint return."
The document is only
available in pdf, so I can't post a direct link here, but you can access it
from 2018 INDIVIDUAL INCOME TAX FORMS;
open the "IN-529" link to find the form and its instructions.
