In reply to @matejc:matrix.matejc.com
I have no clue on how to do it with official Proton 10, but with Proton GE 10, you can just set PROTONENABLEWAYLAND=1 before launching a game

anyways, here's the config:

  jovian = {
    steam = {
      enable = true;
      user = "codebam";
      autoStart = true;
      desktopSession = "plasma";
    };
    devices = {
      steamdeck = {
        enable = true;
        autoUpdate = true;
        enableControllerUdevRules = true;
        enableSoundSupport = true;
        enablePerfControlUdevRules = true;
        enableOsFanControl = true;
        enableDefaultStage1Modules = true;
        enableFwupdBiosUpdates = true;
        enableGyroDsuService = true;
      };
    };
    hardware = {
      amd = {
        gpu = {
          enableBacklightControl = true;
          enableEarlyModesetting = true;
        };
      };
    };
    steamos = {
      useSteamOSConfig = true;
    };
  };

anyways, here's the config:

  jovian = {
    steam = {
      enable = true;
      user = "codebam";
      autoStart = true;
      desktopSession = "plasma";
    };
    devices = {
      steamdeck = {
        enable = true;
        autoUpdate = true;
        enableControllerUdevRules = true;
        enableSoundSupport = true;
        enablePerfControlUdevRules = true;
        enableOsFanControl = true;
        enableDefaultStage1Modules = true;
        enableFwupdBiosUpdates = true;
        enableGyroDsuService = true;
      };
    };
    hardware = {
      amd = {
        gpu = {
          enableBacklightControl = true;
          enableEarlyModesetting = true;
        };
      };
    };
    steamos = {
      useSteamOSConfig = true;
    };
  };

so I unset the kernel like you said to do in that issue, but the values conflict in modules, so how do I resolve that?

       error: The option `boot.kernelPackages' is defined multiple times while it's expected to be unique.

       Definition values:
       - In `/nix/store/b15p9l85pzy934qvdxvq149wm2771dy8-source/modules/devices/steamdeck/kernel.nix'
       - In `/nix/store/h6f2qc39h0nkjyfrivi1y9gk9sbyhzf6-source/nixos/modules/tasks/filesystems/bcachefs.nix'
       Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.