You do not indicate on the tax return the reason that taxable Social Security benefits are zero. The IRS has not provided any means of indicating that, nor have they said that it's necessary to state the reason. I would think that the IRS would see the foreign address and recognize the situation. If not, and you get an IRS notice, you will have to reply to the notice with the explanation.
For 2023 and later, TurboTax puts the full amount of benefits on Form 1040 line 6a with zero on line 6b. That at least shows the IRS that you are not ignoring the Social Security income.
If you are filing an amended return for a past year, you do have the opportunity to include a short statement of the reason in the explanation of changes that you have to enter on Form 1040-X.
