Thank you, ErnieS0. This is really helpful.
Here is the feedback for the TurboTax behavior that led to this mistake:
In my case (income re-sourced by treaty), the income subject to the double taxation was equal to the AGI. However, the income taxed by the foreign country was larger (it included all the SS benefits plus the stimulus checks). The questionnaire for the foreign income comes before I am aware of the taxable part of my SS benefits. Therefore I entered the actual income taxed abroad and the actual foreign taxes paid.
When the software prompted that only the AGI can be taken into account, I accepted it. No prompts followed that I have to adjust accordingly the foreign tax reported as covered by the treaty, nor the software automatically re-calculated these. Perhaps these should be added. Thank you.
