What does it mean when asked if want to use ur earned income credit from 2019 for 2020 taxes? I've never seen this before?

It's part of the temporary Covid rules.  You are allowed to use 2019 Earned income to calculate EIC ( and additional child tax credit) if gets you more credit than using 2020 income.  Many people had a reduction in  earned income because of being out of work (unemployment comp is not classified as earned income)

The lookback rule is part of the Coronavirus tax relief package.

The special lookback rule will allow lower income individuals to use their earned income from 2019 to determine their Earned Income Tax Credit and the refundable portion of the Child Tax Credit in 2020, since their lower 2020 income could reduce the amount they are eligible for.

Please read this TurboTax blog for more information.