you must use the cash contribution worksheet and enter the amount of "money" i.e. cash contributions. the $300 won't show up immediately on line 10b. apparently, it should appear once you wrap up itemized deductions. until then TT doesn't know that your standard deduction will exceed your itemized deductions and therefore qualify for this deduction.
If you are in TurboTax Online, the screen Charitable Cash Contributions under CARES Act appears as the end of Deductions & Credits. First you have to pass the screen Based on what you told us, the standard deduction is best for you at the end of Deductions & Credits.
But you have to qualify for the standard deduction before the screen appears. So you may want to change the value of one or more itemized deductions to $1 so that you qualify for the standard deduction.
Follow these steps:
At the top of the screen, click on Deductions & Credits.
Scroll to the bottom of the page and click on Wrap up tax breaks.
Continue through several screens.
At the screen Based on what you told us, the standard deduction is best for you, click Continue.
At the screen Any Charitable Cash Contributions? enter the dollar amount.
Continue through Federal Review to make sure that things look correct.
Then restore your itemized deductions dollar amounts.
See also this TurboTax Help.
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