Both online and desktop versions of Turbotax are taking the Iowa low-income exemption when the taxpayer is claimed as a dependent on another person's Iowa state return.
On Iowa tax return Turbotax checks the "Check if using alternate tax (line 5), tax reduction calculation (line 12),
or low-income exemption. See instructions." in step 5, even though Step 2 line 1 "Single: Were you claimed on another person’s Iowa return" is checked as YES.
Iowans cannot claim the low-income exemption if they are claimed as a dependent on another person's return.