I believe it should work like the 1045 https://proconnect.intuit.com/community/individual/help/entering-form-1045-application-for-tentative... It may just be too early in the season for it to be fully functional. 

Yes, you must file the 1120 first. 

I went back to a 2019 return to "test" It looks like PCT does little more than offer you a way to enter figures and create the form. You will have to go back to each preceding year to figure the affect of the carryback and enter it in the 2020 software.