1) Make sure that game recording is turned on using the method above.

2) Launch any game.

3) Press Windows key + G to open the game bar. It may ask you if you want to recognize the current application as a game if it doesn't recognize it.

4) Click on the cog on the far right of the bar to open a settings window.

5) Uncheck 'Open Game bar using (button) on a controller'. Should look like this:

6) Steam is now free to use the button in game. Do a little victory jig.