Steam’s player base won’t factor into your Windows 10 multiplayer experience.
Here’s a rather annoying thing that Windows 10 players who purchase from the Windows Store can’t do in Call of Duty: Infinite Warfare – they can’t connect to the Steam player base, which represents the lion’s share of Call of Duty users on PC.
Activision noted on its official support site that both Infinite Warfare and Modern Warfare Remastered noted that multiplayer servers won’t connect to Steam servers. On the official FAQ, it noted that with regards to playing with friends who own Steam copies, “No, you can only play these titles with other users of Windows 10 on Windows Store.”
It’s a fairly annoying thing to deal with especially since Steam has been the default PC market for Call of Duty for much of the series’ lifetime. Whether Microsoft is working to deal with this or not hasn’t been confirmed. In the meantime, opt for the Steam version if you want to experience either game’s multiplayer the right way.