If you like to play your Steam games in Big Picture mode and have upgraded to Windows 10 recently, you may have noticed that the main XBox controller button no longer functions as it’s supposed to. But don’t worry, there is a very simple fix for this and it doesn’t require the XBox app. First bring up the Game DVR systems by pressing:
Win + G
This should bring up the Game DVR bar.
Next click on the Gear (Settings) icon on the far right.
Located the second to last checkbox which reads: “Open Game bar using (XBox button) on a controller” and uncheck it.
Now you’re good to go. Close out the Game DVR settings dialog and give it a try. If all is well you should be able to launch Steam in Big Picture mode and your screenshot shortcuts, etc should all be working now.