No. It is based on 2021. They just used your 2020 return to send the checks out fast.
If you didn't get the full 3rd Stimulus payment in 2021 based on your 2020 income or qualify for more, you will get it on your 2021 return line 30 Recovery Rebate Credit if you qualify based on your 2021 income. See IRS question 2 here,
2021 Recovery Rebate Credit — Topic C: Eligibility for claiming a Recovery Rebate Credit on a 2021 t...
