My suggestion would be to carefully complete MD's own Pension Exclusion Worksheet manually, and see if your results jibe with the TurboTax calculation.
2020 pension exclusion worksheet (marylandtaxes.gov)
If you find that your original MD tax return is incorrect, you can submit an amended return.
A TurboTax bug of this nature would have conceivably affected hundreds, if not thousands, of MD TT users; but judging by the absence of similar questions, that doesn't seem to have happened.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
