You cannot "rollover" a Traditional IRA, 401(k), etc. into a Roth.  You can convert it to a Roth.  Big difference.

There was no 2020 Roth conversion.  The conversion happened in 2021 and you report it as such.  The investment house should have issued a 2021 1099-R for the conversion but I've seen some not do it when it's internal.  In that case use the investment house data from the 2020 1099-R and create your own 2021 1099-R and then on page 2, box B5 of the 1099-R Worksheet mark that the entire amount was converted to a Roth.