How to fix your PS5 or Other Controllers not working on Steam.
I believe after the Steam Deck released, it caused some controllers to not register on load up.
Remember Shift + Tab will get you to your Steam Overlay, then Controller Settings, Enable Steam Input then click on View Layout and then your controller should start working! :)
I have ran into needing to restart the game to get the controller to work as well, after Enabling your controller.
Thank you all! And I hope this helped you out!