Your system information

• Steam client version (build number or date): 1791918634 (build date Tue, Oct 13, 2026 20:44 GMT)
• Distribution: NixOS, Linux 7.2.10
• Opted into Steam client beta?: No. I tried both, same result.
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• GPU: AMD RX 7900 XTX

Please describe your issue in as much detail as possible:

The Steam Controller (2026) works everywhere inside Steam, but a game never receives input while the client runs as the experimental SteamRT3 client. Turning that off makes it work, and I can flip between the two states.

I run FINAL FANTASY XIV via XLM compatibility tool, which starts XIVLauncher.Core and runs the game with its own wine build and DXVK. Proton games are unaffected and work either way.

Steam's side looks healthy while the game is running with the toggle on:

• /proc/bus/input/devices contains "Microsoft X-Box 360 pad 0", so the virtual gamepad is being created.
• controller.txt shows "Queueing activation for controller: 0 app: 39210" (FINAL FANTASY XIV), not just 413080, so Steam Input engages the game's config.

The game sees an Xbox controller, but doesn't detect button presses. I have a virtual menu on left touchpad with keyboard presses, those work.

Controller: Steam Controller (2026), firmware current, connected wirelessly through the charging puck (28DE:1304, serial FXB99602002E2).

No difference from: the Steam client beta or STEAM_COMPAT_RUNTIME_SDL2=classic on the game.

Steps for reproducing this issue:

1. Enable "Use experimental SteamRT3 Steam Client" in Settings -> Interface -> Advanced. Restart Steam.
2. Force XLM as the compatibility tool for FINAL FANTASY XIV.
3. Launch FFXIV with the Steam Controller (2026) connected and in gamepad mode.
4. Verify controller is not handled correctly.
5. Turn the toggle off, restart Steam, repeat. The controller works.