you can just add German SSA income to the normal SSA USA entry (if you get both, just add them manually)
Same is true for anyone with Canadian SSA, these are the only 2 countries that this works for.
btw, there is not a different tax for SSA, it just that not all SSA income is fully taxable, the amount taxable depends on you AGI and at most its 85% of SSA, less if you earn less total
I am not a TAX professional, just have my experience as tax prep volunteer
