Notice the * (asterisk) next to line 15c. That means that the line 6-12 calculations were done on the "Taxable IRA Distribution Worksheet" instead of the 8606 form per the instructions in the IRS Pub 590B (Worksheet 1-1) https://www.irs.gov/publications/p590b#en_US_2019_publink1000270091.
You can print all forms and worksheets to see that worksheet in TurboTax online.
(TurboTax sometimes uses that worksheet even when they do not need to, but that does not change the final calculations and taxable amount.)
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
This answer has been verified for accuracy by an Intuit expert employee
