When you added the nondeductible traditional IRA contribution for 2019, TurboTax switched to using Worksheet 1-1 of IRS Pub 590-B to calculate that taxable amount; Worksheet 1-1 adds the $3,500 of new basis to the original $11,000 of basis:
$7,947 * $14,500 / ($7,947 + $160,697) = $683
resulting in a taxable amount of
7,947 - $683 = $7,264
Commentary: Worksheet 1-1 is supposed to be used only when your traditional IRA contribution "may not be fully deductible and [you] have to figure the taxable part of your 2019 distributions to determine your modified AGI." I think that TurboTax uses this worksheet more liberally than intended. I think it's inappropriate for TurboTax to use this worksheet if it's certain that none of your traditional IRA contribution is to be treated as deductible and, therefore, the worksheet is not needed to determine your MAGI, as is the case here. It's my opinion that this worksheet should only be used when MAGI in in the phase-out range for a deduction for the traditional IRA contribution and a deduction will be claimed.
