There have always been borderline cases, always, going back to the Prop 48 days of Chris Zorich and Tony Rice. Hell, going back to the Gipper. (And certainly going back to, say, Tee Shepherd and Aaron Lynch in the early BK years).
I think what SeekNDestroy said is basically correct, that they assess whether a recruit can graduate from Notre Dame, and decide from there. It’s probably as much an assessment of a recruit’s character and life goals as it is their academics, beyond a certain base line anyway. Given the academic support Notre Dame offers, if a kid wants to get his degree they can help most of them make it happen (and I don’t mean by cheating!) But they have to want to.
If anything, making that assessment may have gotten easier in the NIL era since the kids who don’t want to “play school” to begin with really don’t have to any more. We can go get the ones who do.