The IRS's note for line 4 of Form 8606 is clearly inconsistent with the IRS's calculation on Worksheet 1-1 of IRS Pub 590-B since Worksheet 1-1 includes on line 2 the amount of any contributions made in 2020 for 2019 and treats them as nondeductible. Because of this, Worksheet 1-1 will always produce a taxable amount that is less than or equal to the amount calculated on Form 8606 (contrary to the assertion in the original question).
It's my belief that TurboTax uses Worksheet 1-1 excessively, including in cases where there is no question that the contribution made in 2020 for 2019 is entirely nondeductible, either because the MAGI would be above the threshold for any of the traditional IRA contribution to be deductible even if AGI was reduced by the entire amount of the traditional IRA contribution for 2019 or because the individual elects to make the entire contribution nondeductible. In these cases, Worksheet 1-1 is unnecessary. I believe that Worksheet 1-1 should only be used if the traditional IRA contribution might be only partially deductible, with the deductible amount depending on MAGI. (I think that the instruction for the use of Worksheet 1-1 should say, "Use only if you made contributions to a traditional IRA for 2019 that may be only partially deductible and have to figure the taxable part of your 2019 distributions to determine your modified AGI.")
