Why did Turbo tax calculate a 4198 refund and actual refund was 1398 for 2021 taxes?

Did you receive $2800 in the third stimulus payments (EIP3) several months ago, but reported on your return that you didn't receive them?   If the IRS believes they paid it to you already, they would take it off your return.

Is $2800 showing up on your Form 1040, Line 30 (Recovery Rebate Credit)? 

Also see if there is a clue at the IRS "Where's My Refund" tool:

https://www.irs.gov/refunds

If the IRS reduced your refund, you should get a letter from them in 3 weeks or so explaining why and what recourse you have if you disagree.

what is on Line 30 of your tax return?  sounds like you reported that you did NOT receive the 3rd stimulus, but the IRS thinks you did. that is why the refund adjustment

2,800 is the 3rd Stimulus payment.  Did you already get the Stimulus payment they sent out last year starting March 2021? The IRS has records that show you were sent the 3rd stimulus payment so they removed the 2,800 Recovery Rebate Credit.

 Do you have an amount on 1040 line 30?  You might have tried to claim it again.   Line 30 is only if you didn't get the full amount or qualify for more. 

Did you get IRS letter 6475 saying what they sent you?  If you didn't get the IRS letter 6475 saying what they sent you then Double check your bank statements and check your IRS account to see what they sent you.  Check both IRS accounts if married.

Your Online Account | Internal Revenue Service

don't feel bad. I'm guessing that Turbotax has over 5 million users and by the number of threads about a missing $1400 or $2800, I'm guessing a million made the same mistake.