I have seen cases where a taxpayer forgot that they had received a stimulus and claimed it on their 2020 return. Also there were people who were mailed a check and never received it. And people who received the stimulus on a debit card and threw it away because they did not know what it was.
If there was no explanation give to you, you can contact the IRS and find out why you did not receive the stimulus amount that TurboTax calculated. They may need to trace a payment that you did not receive.
