Retirement tax questions

Yes, you can enter it if the contribution and conversion happen in different years. You will enter the basis from prior years either in steps 8 and 9 (if you have another contribution) or in steps 7 and 8 (after you enter your 1099-R).

TurboTax will ask about value on December 31, 2020 of all traditional IRAs after you enter the basis during the 1099-R section interview. This will be used to calculate the taxable amount.