If you are using TurboTax Online follow the instructions for interview or Step-by-Step mode, the experience I found is to answer Yes, I have Residential Energy Property Expenditures, then No the home is not in the U.S. which then causes 21a to be checked No and the IRS won't reject for the empty line 21a.
Please see the rest of the instruction about the IRS will not reject your return.
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