Entering stimulus amounts in the "Federal Review" area will not lower your refunds. However, please note "Federal Review" is the final section of the federal return interview. Once you click through that section, your information will transfer to your state return. When that happens, your state refund amount may change based on all your entries in the federal sections at that point.
Yes you can see your refund or tax due change when you enter the Stimulus payments. Your 2020 return starts out by assuming you didn't get any Stimulus payment so it gives you the full amount. Then near the end you enter how much you actually got so it only gives you the difference if any. You don't get it twice.
Check line 30. The Recovery rebate credit is on 1040 line 30. It either adds to your refund or reduced a tax due.
Before filing, You can preview the 1040 or print the whole return
Let me explain how stupid the placement of the stimulus question in the interview flow is ... until you get to that point the program was including the entire stimulus credit you are eligible for based on your 2020 return but when you finally tell the program how much you already got in advance that same amount is removed from the estimated refund posted.
It would be nice if they would have asked for that information in the beginning in the MY INFO section BEFORE you entered in the income BUT the programmers did not ASK us posters in this forum AND they probably will not listen to us now and change the interview flow so I will be posting this answer A LOT this year.