If the IRS reduced your refund, they will send you a letter explaining why. You might not get the letter until a few weeks after you received the refund. TurboTax does not get any information from the IRS about why your refund was reduced.

That is probably  the $1,200 stimulus that you said that you did not receive so it was added to your refund but the IRS records show that you did get it already so they removed it.

Was there $1,200 on 1040 line 30 for the Recovery Rebate Credit?  The IRS has been adjusting returns that claimed it but the IRS already sent it.  Did you get it after you filed?