TurboTax is apparently using Worksheet 1-1 from IRS Pub 590-B to calculate the nontaxable and taxable amounts of this Roth conversion rather than doing the entire calculation on Form 8606, indicated by asterisks on lines 13, 15 and 18.
https://www.irs.gov/publications/p590b#en_US_2019_publink1000270091
