Line 26 has nothing to do with tax deductions. It's for estimated tax payments and overpayment from your 2023 tax return that you elected to apply to your 2024 estimated taxes. If you need to enter estimated tax payments, there is a separate section for that under Deductions and Credits that populates TurboTax's Tax Payments Worksheet. Itemized deductions go on Schedule A and tax credits go on Schedule 3.
I'm not sure why the explanation statement that appears when you click the Explain button next to Form 1040 line 26 is being identified as being for Schedule 3 line 8, but that Explain button is only for providing an explanation statement if you changed your name and had made estimated tax payments under your former name. Nothing else requires explanation with respect to line 26.
