@skinnylatte MAYBE something like this will work https://www.amazon.com/ATCCPYDM-Capture-Loop-Out-Compatible-Windows/dp/B0CKHB1C2B -- looks like it has an analog capture device (it supports VGA), so you could probably have the macbook output in a quicktime window or something like that.
But I'm guessing the trick more generally is that you need an analog DVI input, and most modern monitors don't have the ADC in it.