When you are completing and e-filing a tax return, TurboTax will send it through their error checker looking for inaccuracy when you are in the process of completing it. Then, once you are able to e-file it, it is sent to the IRS and IRS either accepts it or rejects it.
IRS will send you a letter regarding the reason they changed the refund amount you requested. There is no way that TurboTax has any control over that or would even have any information as to why IRS reduced your refund.
One area that some people are finding that happening is when they say they did not get the second stimulus check, file their return, and then they receive the check from IRS. IRS has been verifying the returns saying they did not receive the second stimulus check with their records and if they don't match, they are adjusting the refund amount.
