To enter the amount you paid with an extension (including state extension) go to
Federal Taxes (or Personal Tab for desktop H&B version)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Update button
Next page second section Payments with Extension
Either Visit All or Click Start or Update by the extension you paid
For 2024 Federal Extension payments should be on schedule 3 line 10. And go to 1040 line 31.
Pay attention to which year you are entering for a State Extension payment. A prior year state extension payment is also deductible on the federal return so be sure to enter them on the right lines.