The Form 1099-R also has box 2b Taxable amount not determined marked to indicate that the IRA custodian has no way to know if you've made any nondeductible traditional IRA contributions, only you know that. You were required to report any nondeductible traditional IRA contributions on Forms 8606 for the years for which such contributions were made, with line 14 of each of those forms carrying forward to line 2 of the subsequent Form 8606. If you had reported everything correctly, the amount on line 3 of your 2022 Form 8606 will show $12,000.
TurboTax saying "Good News: You don't owe extra tax on this money" is just acknowledging the that code 2 in box 7 of the Form 1099-R means that the conversion is not subject to an early-distribution penalty, which is an excise tax.
