This isn't exactly what you described, but are you thinking of
538's simulator?
I find it useful, although I'm more optimistic on Cincy than it is--my view is if they win out (definitely not a given), they're more than 82% likely to make the playoff. Historically, getting in the playoff correlates better with strength of record than various power indexes (as IMO it should), and Cincy is still #2 there. Excluding last year, which had strange COVID effects, I believe only 2014 TCU (#4, replaced by #6 Ohio State), 2018 Ohio State (#4, replaced by #6 Oklahoma), and 2019 Georgia (#4, replaced by #5 Oklahoma) have been in the top 4 and not gotten into the playoffs.