Terarria, it's a fun 2d game similar to minecraft but with more combat. Co op too so you could play with him.
Children of Morta, a diablo esque game with fun combat and decent story. Graphics are more pixel and less high res, so might give him that nostalgia factor. Also has co op.
Hollow Knight and Dead Cells, 2d platformers with combat, they are a bit difficult at times but still quite fun.
Minit, basically a zelda clone, but with a 60 second mechanic, you go as far as you can in that 60sec and then "die". During those 60sec you might find a key or tool that lets you open a path or door, progressing further next time etc.
All of these are on gamepass. Might be worth getting him a sub for a month to test the waters.
This post was edited by jlhromeo on Feb 10 2020 12:15pm