we don't know the country or whether you're an expat.
Basically, the US foreign tax credit is based on a ratio of net taxable foreign income to US taxable income times the US taxes. Since you say by treaty the none of the pension is taxable in the US, you should be getting zero FTC.
line 1 of form 1116 (general category) would be zero because that only reports the taxable portion of foreign income
thus line 7 would be zero
line 14 is available foreign taxes
line 15 is line 7 = 0
line 17 is line 15 + 16. assuming line 16 is zero line 17 =0
line 18 is your taxable income from 1040 line 15
line 19 divide line 17 by line 18 = 0
line 20 is your taxes reduced by certain schedule 2 credits
line 21 the FTC you allowed is line 19 times line 20 = 0
line 23 is zero assuming line 22 is zero
line 24 is the smaller of line 14 or 23 which would be line 23 or zero
