Thanks, I appreciate all this info.  I did check all of this out before coming to this site. The MFS spouse who Lacerte has as NOT claiming the child is having to pay back the $900 Adv CTC, but then the MFS taxpayer who is claiming the child is getting her half (again) AND and an additional $1800 "Additional Child Tax Credit" and the $700 Recov Rebate for the spouse's half of the child's Recov Rebate (that the spouse did indeed receive, but doesn't have to pay back.)

Form 8812 instructions are silent as to whether the credit gets halved for MFS. And yes I do know that even though 2021 Pub 17 says to halve the credit for MFS that we are supposed to look to the 8812 to calculate the credit. (The 2020 Form 8812 instructions also do not state anything about halving the credit.)

It just seems like it is a way to game the system. Hmm.