I am having this same issue. The MFJ vs. MFS comparison is showing a tax savings due to this issue. I have MFS vs MFJ comparison and living together (in a community property state) boxes check.  Also, Lacerte is not cutting the Child Tax Credit in half on the taxpayer who has the child on his MFS return.  On the Form 8812, it is giving the MFS taxpayer the full $3600 for the child who is under age 6.  Shouldn't it be half that, $1800?  It still states in Pub 17  for 2021 that the CTC for MFS is half.  Unless I missed something?