Sorry for the late reply. It’s been a long time since I played Steam on an actual computer so I’m not finding where the developer settings I mentioned earlier are located.
Edit: You mentioned trying two different controllers. Have you tried to have both plugged in at the same time so that the game can see both?
While you have the game running, are you able to open the Steam Overlay?
In the overlay, click on the controller icon
In the settings here, do you have an option to reorder controllers on the right side of the screen?
If you see that button, click on it and mess around with the controller order and see if it'll make the game see the controller now.
There’s some good ideas in that thread. I like the ones of remapping from clicking joysticks to one of the back paddles. Currently I have an action set to bring up the on-screen keyboard if Steam + X isn’t working that day.