Does the IRS require a specific stated date your business closed, and why you're closing, when filing a "final" Sched. C (sole proprietor) for 2024 tax year?

The IRS doesn't ask for a specific date when the business was closed as long as it was closed before 12/31.  For California, when reporting your business, the same applies when reporting your income and expenses.  For California, you might also have other required filings to close the business.   Go to Closing a California Business Entity for more information.  

In TurboTax, go ahead and continue the entries as if you were reporting income and expenses from your business.  TurboTax will ask if you stopped your business, and will ask for more information on how to closed the business.  You will still have to go through the interview process for the business. The program will ask about income and expenses, and about any assets that the business had.  

For more information visit the following links for both IRS and TurboTax information on closing a business:

Steps to take to close your business

Closing a Business