TurboTax Deluxe 2021 (download) on 1040/1040SR Worksheet, line 12b has a possible bug

on 1040/1040SR Worksheet, line 12bPossible line 12b bugPossible line 12b bug
Line 12b is auto filled in as $300, even though I entered $500 for cash donations (somewhere else) made with 5 repeated $100 donations. The $300 is flagged as an unacceptable value, even though I'm married filing jointly. I think it should be $500 in my case since I'm allowed up to $600 as a married filing jointly.