This solution comes from some good people who were kind enough to help out in the game's Discussions/Bug Reports community section.
See the original post here: Original discussion bug report

You load up the MASS Builder game, you DO NOT see the little popup message in the corner of the screen that says "Controller Configuration Loaded", and the gamepad/controller input is not recognized by the game at all, even though it clearly works fine for other applications. You can still play with the keyboard and mouse, but dang it you really want to use your controller!!

Exit the game, to the desktop.
Open your Steam Library.
Find the MASS Builder game on the list.
RIGHT-click on the game on the library list.
Select "Properties."
On the "General" tab...
There is a drop-down selection bar you can use. Default is set to "Use your Steam global setting".
Change this setting to "Forced On."

What this does is tells Steam that no matter what Steam's current general rule about controller settings is, this game is supposed to ALWAYS use the controller layout profile. This will not affect that setting for your other Steam games, only this one. Here is an image to illustrate. Obviously your library list will be different from mine, but focus on what's circled or arrowed in PINK highlighter.



Restart the MASS Builder game.
You should now see a Steam popup window (usually in the bottom right corner of the screen) that says something to the effect of "Controller Layout Profile Loaded." Now when the game gets to teh main menu screen you should notice that the controller functions properly.

The one who originally posted the problem in the bug fix discussion thread: "Biscuit | WFH"

The one who posted the solution there: "zapoqx"



Again the original discussion thread is found HERE.


Since I did not discover this solution on my own, please direct any comments/questions to that discussion post. I'm just posting this guide to help make the solution a little easier to find for people who try searching for a GUIDE first. Happy gaming!