Your 2021 tax return should have included Form 8606 reporting the $6,000 nondeductible traditional IRA contribution on line 1. The $6,000 will fall through to line 14 which carries forward to your 2022 Form 8606 line 2 and your $19,000 after-tax basis would be added to that for a total of $25,000 on line 2 of your 2022 Form 8606. Of course this change to line 2 affects the pro rata calculation that follows, so the nontaxable amount of the Roth conversion will be higher since is includes a large portion of your basis in nondeductible traditional IRA contributions.
Using Worksheet 1-1 from IRS Pub 590-B, TurboTax will also likely include the $6,000 contributed in 2023 for 2022 as part of your basis in nondeductible traditional IRA contributions used in doing the pro rata calculation.
