Steam game controllers only sometimes work

[octoturt]

On my X1E device running Ubuntu 25.10 (with FEX using the Ubuntu 24.04 LTS image), I've gotten inconsistent results between Steam games running under FEX. I've tested multiple controllers and encountered significant issues using Xinput, but with Dinput (on my 8BitDo Ultimate 2 controller, over Bluetooth and 2.4ghz USB), the controller works perfectly in Steam Big Picture. However, different games react differently.

• Portal, a game which natively runs on Linux and uses Steam Input, fully supports my controller. All buttons, the sticks, and the gyroscope are fully functional in-game. I cannot open the Steam Overlay, but I can use the standalone controller settings window to configure it
• Celeste, a game which does run on Linux but does not use Steam Input, shows button prompts in-game, but doesn't react to any button presses. Attempting to open the Steam Overlay results in a severely corrupted screen until it is closed
• PuyoPuyo Tetris 2, a game which runs under Proton and does not use Steam Input, does not give any indication that a controller is connected, and the Steam Overlay cannot be opened

Attached are the output I could get from each game as it launched. If there's anything else I need to provide, please let me know.
portal.log
celeste.log
puyopuyotetris2.log

[Sonicadvance1]

This is likely a duplicate issue of this

Gamepad input is broken for 32-bit processes, this includes steam input because steam (a 32-bit process) reads the inputs and then passes them to the application.

[octoturt]

The Steam client is reading inputs fine, though? I can use the controller to navigate in Big Picture mode, and use the controller config menu. I believe Portal is also 32-bit, but despite that, it was the only game where my controller worked, while Celeste and PuyoPuyo Tetris, both 64-bit titles, fail to accept controller input.