Let's walk thru the steps you took to amend the return... 1) you entered the return the same as the taxpayer had  2) You went into Form 1040X and checked the 2020 Box so the original information populated the form 3) you made the changes required      This should have created the 1040X required for efiling.

ProSeries just made available the ability to amend a return that was not originally prepared by you - have you updated the program recently?