It is too late to file an extension. They had to be filed by July 15, 2020. Just file your return as soon as possible. If you are getting a refund there is no penalty. You can efile until Oct 15. After that Turbo Tax Online will close for 2019 returns and you will have to mail it.
It is too late to get an extension for a 2019 return. Now your return is just late. If you are getting a refund there is no penalty for missing the filing deadline.
If you owe tax due, then you will be subject to late filing penalties and interest on the the amount you owe
If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.
"Somehow, I thought things had all been pushed back to October..." You misunderstood. The original filing deadline was April 15, 2020 and was pushed to July 15, 2020. People who did request extensions have until October 15 to file their tax returns--but still had to pay tax due by July 15, 2020. The last day to e-file your 2019 return will be October 15, 2020. After that, e-filing will shut down and you will have to file by mail.