I doubt any of Microsoft Game Studios seriously use Blender, although I'm sure some individuals might use it for specific workflows. AAA games almost universally use Maya (and ZBrush, Substance and Houdini), for example this presentation on Gears 5 workflow specifically mentions Maya and Houdini (https://cdn.gearsofwar.com/thecoalition/publications/The%20V...). This donation specifically mentions digital humans created for Microsoft Research, and MS Research as the user, not Microsoft Game Studios.