Why didn't Turbo tax use my 2020 income to file my 2021 taxes since my 2020 income was lower. Wouldn't this have resulted in a higher tax return?

[Bsch4477]

There’s no provision to use 2020 income. You might be thinking of using 2019 earned income for calculating earned income credit if the 2019 earned income is greater than that in 2021. 

[DawnC]

No.  There is no option to use your 2020 income numbers.   You can use your 2019 earned income to figure your 2021 earned income credit (EIC) if your 2019 earned income is more than your 2021 earned income.   This is called the lookback provision and it does not use any 2020 figures.