I tried contacting steam support about this, they told me they can't help and my only option is to make a post on the forum.

I have been using my Steamdeck as a controller to play games on my computer (Elden Ring) for several weeks.

A week or two ago however, this no longer functions. I launch the game on my desktop, wait until it loads to the home screen, and then I click Connect on my Steamdeck. Once connected, the game simply receives no controller inputs from my Steamdeck. I can use keyboard & mouse without issue. It's worth mentioning I have the buttons on the back of the Steamdeck custom-bound to the arrow keys on my keyboard, and if I press those back buttons the game does receive the input.

I am on Arch Linux. I was running the game using Proton-GE originally, but since the problem occurred I have also tried using Proton Experimental and Proton 9.0-2. I have tried using beta releases of the Steam client on both my desktop and Steamdeck.

I tested to see if this was game specific, and it was not. Same problem on any game I launch.