I wonder if it is because of this change:
4.11-3:
Games will now attempt to access gamepads directly, instead of Proton emulating gamepads as if they were Xbox controllers. This means PlayStation 4 gamepads as well as fighting gamepads and other controllers will behave much more like they do on Windows. If you would like your gamepad to be emulated as if it were an Xbox controller, please use the Steam client controller mapping feature. If the controller cannot be accessed directly, due to a permissions issue, it will continue to be presented like an Xbox controller.
However aren't PS3 Controllers seen as Xbox controllers by games due to the HID-Sony mapping it that way?
Manually setting the controller buttons in steam input fixes it.
proton 4.11x1 2020-11
Compatibility Report
System Information
I confirm:
Symptoms
The DPAD of my PS3 Controller won't work with proton 4.11 and above. If I switch to 4.2 the DPAD works fine. All other buttons work.
Reproduction