Line 9b IS limited to the $10,000. However, do not use the 10,000 in the formula when calculating what 9b would be if there were no limit. In other words:
Form 8960, Line 8 / AGI x SCH A*, Line 5 = Line 9b. If this 9b is over 10,000, you have to put 10,000 on Line 9b. I used TaxAct last year and it did not put the 10,000, so I had to manually over-ride it.
You may also use Line 9b even if you take the Standard Deduction. I have spoken with a CPA (who does taxes) and a second Tax Expert who both say you can do this. I have also read a reddit forum that states this as true. The person from the forum believes the Tax Law allows it, the IRS instructions do not. You need to go to Forms (if you have the downloaded version) and manually over-ride it.
* My question is, in the formula above, where it says to use SCH A, I'm not sure you really can. Can you include the portion of taxes paid in 2020 for 2019? I have read varying opinions.
