The instructions for Line 3b on page 16 of the Instructions for Form 1116 state:

"Enter on line 3b any other deductions that don't definitely relate to any specific type of income (for example, the deduction for alimony paid from Schedule 1 (Form 1040 or 1040-SR), line 18a)."

In your explanation, you would describe what these deductions are.

I got this too - the first answer is less than helpful if you did not, in fact, come up with the "other deductions" value in the first place, is it!?

Best I can tell, this value was derived from the Foreign Tax Credit Computation Worksheet, which TT fills out on your behalf when answering the questions about what countries the tax went to.  Line 3(b)(1) has the amount that need explanation - and I have no idea where that amount is computed from!  Not only that, it won't let you override, nor trace its source.

So if someone could be helpful and point us to where this mystery # comes from, maybe we can solve this for real.

thank you!

OK, more searching and I found this post: https://ttlc.intuit.com/community/tax-credits-deductions/discussion/form-1116-explanation-statement/...

Basically for me this amount came from a self-employment sheet I had filled out due to a 1099-MISC payment. So it might be a "Deductible part of Self Employment Tax" or other item like that. I used the comment just to move on, as I don't think the amount changes anything. It would just be nice if clicking it would tell you where it came from!