Don't change anything on your W-4 ... this was an unusual tax year.
Look at the form 8812 & the 1040 ... note that the tax bill of $6632 on line 24 is being paid with the withholdings on line 25d + the CTC on line 28 which gives you a refund of line 35a. The form 1040 is one long math problem ... follow the calculations on the 1040 & 8812. If they did not give you the $6600 in advance your refund would be $6600 larger.
When reviewing the 2020 vs 2021 return understand that last year the CTC was only $2000 per child ($8000 for 4 on the 2020 return) which paid down your tax bill. This year it is $3000 or $3600 but you got 1/2 in advance which means there was only $6600 on the 2021 return to pay off the taxes ... so naturally your refund will look about $1400 less than last year.
