Why, Just finishing Fed return and on review it has me stopped at not allowing me to enter $300 on line 10b per the Cares Act with standard deduction?

Delete any amount that has been entered in the Cares Act area. 

The key is to enter the cash donations made in the regular section, even though you will not be itemizing. When prompted for the Cares Act above-the-line donation, there will be an amount entered automatically from this entry.

Otherwise, the program treats the entry directly into the Charitable Donations for Cares Act without other details in the donations section as an override.

To fix this in TurboTax, follow these steps:

Step 1: Delete the Charitable Organization donation sheet

• From the left menu, select Tax Tools.
• Select Tools.
• Scroll to Delete a Form.
• Scroll to Charitable Organization and select Delete, Delete Selected Form, and Continue.
• Select Federal from the left menu to return to your program.

Step 2: Re-add the Charitable Organization cash donation entered.

• Enter Charitable contributions in the search box.
• Select the Jump to link in the search results.
• Answer the questions in the interview.
  • Only Money donations count toward the above-the-line deduction when taking the standard deduction. This entry does not need to be detailed. 
• Complete the interview process by answering all donation questions and scrolling to the end of Deductions & Credits to select Wrap up tax breaks.
• Select Continue at Based on what you just told us, the Standard Deduction is best for you.
• At Charitable Cash Contributions under Cares Act, you will see your full cash contributions already input in the box. Do nothing to this cell. Select Continue and Continue.

This process will allow you to claim up to $300 for all taxpayers except married filing separate, who would each have a maximum of $150 without itemizing deductions in 2020.