Something it messed up with the way TurboTax is handling this in that TurboTax is thinking that you used the Last-Month Rule in 2020, but you did not. I don't think that it has anything to do with the way that you used 2020 TurboTax to prepare your tax return but instead is due to 2020 TurboTax inappropriately treating this as a use of the Last-Month Rule all by itself or 2021 TurboTax not calculating the correct contributions limits for 2020 without using the Last-Month Rule.
