Nondeductible contribution in 2021 is moved to Roth. Why is is being taxed, accdg to TT? What is the correct way to enter this?

Our IRA basis for 2021 is both 0 and since my husband's 2020 non-deductible contribution was converted in 2021, basis was understandbly $6000.  It seems incorrect that we are being taxed for contribution in 2021 that was never deducted.