I can't give you a definitive answer, but this can help you look at the entry for line 10b.
Click Tax Tools on the left side bar
Click Tools from the drop-down
Click the "Topic Search" box on the screen
Type or scroll down to standard deduction and exemptions
The next screen gives you an option to change your selection from Standard to Itemized and back. You do not need to change your selection
Scroll down to the bottom of that screen and click CONTINUE
The next screen is the Charitable Cash Contributions under Cares Act screen
IF YOU ARE CLAIMING STANDARD DEDUCTION enter the amount of cash contributions you made, up to 300
IF YOU ARE ITEMIZING DEDUCTIONS enter 0
Scroll down and click Continue
Click Continue on the next screen
The new "up to $300 above the line cash charity donation" is available for tax year 2020. This allows a Taxpayer to claim up to a $300 credit which is subtracted from income on the 1040 line 10c if the Taxpayer is claiming the Standard Deduction. (If you Itemize Deductions, all your donations will be listed on Schedule A.)
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I am trying to transmit my federal tax but it will not let me get past the charitable contributions. I donated $714 in cash. Using the standard deduction, I should be able to claim $300. But it will not advance me no matter what I try. It shows the $714 (as itemized) and then the $300 in line 10b.