I think the credit goes against one’s 2020 taxes.
2019 was just used as an estimate.
Congress chose the 2020 tax year to pass out stimulus money. Since taxpayers hadn’t filed it yet, they used the 2018 and 2019 tax years as the baseline to get eligibility, addresses, and bank account info.
That’s why so many elderly and disabled that no longer need to file taxes did not get a stimulus payment. They will need to file a “Not Required to File” tax return to get the credit paid to them. Privacy rules keep the IRS from getting certain taxpayer information from other agencies, such as the VA system and Social Security payments.
When they want to, federal bureaucrats will listen to laws and the rules they are supposed to always obey.
The first two stimulus payments were passed during the 2020 tax year. The next stimulus, if approved will be disbursed as part of the 2021 tax and budget season.