With this guide, you will be able to play Diablo Immortal on Steam Deck without much trouble. You will also find the controller layout. I tried running the game using different Proton – 7.0.2, Experimental and GE. Unfortunately the game automatically closes when I try to launch. The best and easiest way for installing this game is Lutris.
UPDATE:
If you want control over the FPS and Hz limiter then a Reddit user found a way to manually install Battle.net and Diablo Immortal via Steam without using Lutris. Link to the tutorial: https://www.reddit.com/r/SteamDeck/comments/v3j8uu/installing_diablo_immortal_on_deck/
Go to Desktop mode. First, don’t use Lutris downloaded from Discovery – it doesn’t work properly on Steam Deck and has issues with Vulkan drivers and Wine. Before the next step, make sure it is not installed – if it is, remove it.
Run Konsole and:
Add the Flathub Beta repository if not already enabled flatpak remote-add flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo flatpak update --appstream Install required dependencies from Flathub (non Beta) flatpak install flathub org.gnome.Platform.Compat.i386 org.freedesktop.Platform.GL32.default org.freedesktop.Platform.GL.default Install Lutris flatpak install flathub-beta net.lutris.Lutris
Run Lutris when it’s ready. Click on “+” and “Search the Lutris website for installers”. Type Battle.net and install it. Make sure that “Create Steam Shortcut” is ticked so you can run the game comfortably from Game Mode. When it’s done run Battle.net, log in to your account and download Diablo Immortal.

You can now go to Gaming Mode and start the game. You can find it in your library under the “non-steam” tab. Battle.net will start automatically and all you have to do is click “Play”.
Unfortunately, there is no way to force the game to detect Steam Deck as a gamepad.
I created a comfortable layout for Steam Deck emulating keyboard and mouse. I played with it for a few hours and although it wasn’t as comfortable as a classic gamepad it was good to play.

You can find this layout as “Diablo Immortal Great on Deck” for Battle.net app.
Layout id: 2816677573
steam://controllerconfig/2207814237/2816677573
For more comfort, I recommend turning on automatic item pick-up in the game options.
In terms of performance, the game runs at medium settings around 60FPS with dips to 40 during large battles. There is also some stuttering, but it doesn’t bother me much. Refresh rate and frame limit settings from SteamOS don’t work properly with Lutris installation. If you want you can set 30FPS limit in the game options.