The result suggests that the amount on line 14 of your 2020 Form 8606 (should be $6,000) did not carry forward to line 2 of your 2021 Form 8606. Go through the IRA contribution section again, indicate that you made and tracked nondeductible contributions to your traditional IRA, then make sure that your total basis as of December 31, 2020 shows $6,000. (Your 2020 contribution made in 2021 is treated by law as if it was made on December 31, 2020; TurboTax's wording is misleading.)
