Conversions are taxable events for the tax year equal to the calendar year in which they occur.
Because the conversion won't happen in tax year 2021, your tax forms (8606, 1040, etc.) for TY2021 won't include the conversion. Your Forms 8606, 1040, etc., for TY2022 will include the conversion if you do it in 2022, assuming no change in the current law....