I think the Xbox App somewhat serves content through the Microsoft Store, I definitely had to troubleshoot between the two for a couple things.
They do sell games as well. I think I got an episode of the Batman Telltale series through it for free, though much like Epic managing an additional library with less features/support is usually not worth it for me.
It works! Looks like some people have run into issues with EAC but it worked without finicking around for me.
https://www.protondb.com/app/1172620