The amount on the 1040SR is -$,$$$ - on line 11, the current amount is $0 which TT says is too LARGE? No amount on line 11 clears the error ( or -). What does go here?

It depends. Your self-employment tax deferral section must be updated to resolve this error. When the section was initially completed, you may have not been in a refund position. However, once you were eligible for a refund, this section needed to update. 

Option 1:

Leaving this field completely blank is an option. The system can update with leaving this field blank. As always, it can be useful to close out of your program and close the browser window completely. Re-open in Chrome.

If you are still experiencing unexpected results, then try Option 2.

Option 2:

You can recalculate the deferral by temporarily recalculating this section by adding more income. Otherwise, without any adjustments, you may not get back to the same screens. 

To return to the interview section to adjust these entries and un-trigger any deferral that you no longer want, follow these steps:

Enter a temporary amount as income in the self-employment section that will result in you not having a refund.

1. From the left menu, select Federal.
2. From the Income & Expenses, scroll to Self-employment income & expenses and Edit/Add.
3. At Your 2020 work summary, select Edit.
4. Under INCOME, select Add income for this work.
5. Add Other self-employed income, includes 1099-K, cash, and checks and Continue.
6. At Type of income, enter Temp income to remove deferral and enter a large amount, such as $100,000 and Continue.

Decline to defer any self-employment tax.

1. From the left menu, click on Federal.
2. Click the second tab from the left, Deductions & Credits.
3. Scroll down to Tax Relief related to Covid-19 and Revisit.
4. Select Self-employment tax deferral and select Revisit.
5. Answer Yes at the next screen to get back to Let's start by getting your eligible income.
   1. Enter 280/366ths of your actual income to reflect the income from March 27-December 31, 2021. 
      1. This amount should be the same as the correct amount on Line 18 of Sch SE.
6. Select Continue.
7. At Tell us how much you'd like to defer, 
   1. Enter 0.

Remove the temporary income.

1. From the left menu, select Federal.
2. From the Income & Expenses, scroll to Self-employment income & expenses and Edit/Add.
3. At Your 2020 work summary, select Edit.
4. Under INCOME, select the Trash can icon next to Temp income to remove deferral and Continue.

For more details, see TurboTax Expert @DawnC's answer here, about 2/3 down the page: Resolve Sch SE-T Max Deferral Line 18 must be entered.