If your Maryland Adjusted Gross Income on Line 16 of Form 502 is under the Filing Threshold of $12,000, Lines 17 through 39 are left blank by TurboTax. These lines are left blank because if you don't have any taxable income for Maryland Purposes, these lines do not affect anything on your return.
[Please click the screenshot box below for MD Filing Thresholds for all filing statuses.]
I understand this may be confusing because like you mentioned above, Line 17 says you must select one of the methods. However, I have used several different tax software programs and they all leave those lines blank if your income is under the filing threshold. It may have something to do with the e-filing process that requires that they do this.
Rest assured, your Maryland return is still being calculated correctly and the addition of those lines would not change your refund.
If you have any further concerns, please comment below so I can further assist you.