You're right - it was originally a 2020 credit. And it was either the Paycheck Protection Program or the ERC. Almost every business chose the PPP option...
The ERC was not widely used until March 2021, when the American Rescue Act changed IRS regulations and millions of businesses were now eligible for both the PPP and ERC program by amending their Quarterly Form(s) 941...
The 2020 ERC Program is a refundable tax credit of 50% of up to $10,000 in wages paid per employee from 3/12/20-12/31/20 by an eligible employer.