I'm not including games being exclusive to console only, but rather that there's no real exclusives for series X if they just release everything elsewhere.
Yea series X can play 4 gen , OG xbox, X360, XOne, Series games, and w dev mod can play any older retro games up to gamecube, wii, ps2. Don't think PS5 can even play PS3 yet.
I don't know what you think about games and developers, but Carmack will always be the best developer.
Simply because he figured out how to bypass the limitations of weak hardware using existing developments from other computer tasks and make productive games using only crutches.