lets say youre MFJ with 3 kids and you got the full EIP amounts (7000).
Filing MFS and one of them taking all 3 kids, their RRC would be 5600, but if you split that 7000 in half, thats only 3500, so that MFS person is still entitled to another 2100.

The other MFS half of the relationship, shows they got the 3500 (should have only been entitled to 1400 on the 2021 return), but there is no payback.

As a couple you just came out 2100 ahead.