Hi, 

I'm filing a 990 year change as well.  I just pulled this from the IRS website https://www.irs.gov/instructions/i990#en_US_2021_publink11283jd0e1284: "A short period return filed on the 2020 Form 990 can't be filed electronically unless it is an initial return for which the “Initial return” box is checked. . . "

I will be filing a 2021 short-period return, have you seen anything on that?  

Many thanks. 

Rick