This is what gets me confused: 

All the people, all the articles, clearly state and say that you need to have earned income in 2020 to claim the credit. Even the own IRS Interactive TAx assistant will confuse you when it asks you if you have earned income in 2020, which in the case we are talking, you do not have. And above all: 

Why the software does not allow the efile and marks it as error saying that the EITC was calculated using undocumented sources.