Just tested it myself. Here’s the process that worked for me, in case anyone else needs a guide. No guarantees, of course, but hopefully it works for others too:

From Desktop Mode

Download the Battle.net installer
Add the installer as a non-Steam game
Change the installer settings in Steam to run with Proton Experimental
Run the installer
(tip: to make it easy to find the launcher in the next step, you can change the install path to be in your downloads folder instead of deep in the Proton path)

Once installed, exit the installer
Add the installed Battle.net Launcher.exe as a non-Steam game
Change the launcher settings in Steam to run it with Proton Experimental
Run the launcher
Log in
Install Diablo IV
(tip: uncheck the high res textures option which is on by default to save yourself about 40 GB of space)
Close launcher
(tip: if D4 is the only Bnet game you’re planning on playing, you can rename the launcher in Steam to Diablo IV)

From Gaming Mode

Launch the launcher
Click the Play button on Diablo IV
Enjoy!

Other Tips

During installation or the game, whenever you need a keyboard, press STEAM + X to call it up.

Occasionally, during installation or in the Launcher in game mode, my trackpad input would get wonky or stop responding. When this happens, hold the STEAM button down while using the trackpads, and they should work again.

Beyond that, the game automatically worked from me. It loaded low graphics settings (which are perfect for the Deck) and recognized my controller. It even opens with some accessibility settings before you start playing that lets you scale the font size up too, which makes it easier to read on the small screen.

I can’t say much about how the game actually plays as I really just did this to test if it works. I’ll be putting in my first actual time with the game tomorrow.

I'm primarily a PC gamer with a library slowly approaching 1,000 games on Steam. While I have sometimes bought games through the other storefronts like Blizzard, GOG, Uplay, and EA Origins, I never really invested significant time in them to the point where I don't keep track of what is in those libraries. Suffice to say, I thought that I was so entrenched in Steam that I couldn't possibly play in another storefront for any meaningful amount of time.

This has changed for the past year. I hopped on one of those deals that gave me access to Game Pass since Microsoft added all the Bethesda games and partnered with EA Play. And I gotta say, I'm invested now. Invested so much that I bought a Series X despite having zero interest when the new generation of systems was announced. Game Pass on Xbox is an even better deal than Game Pass on PC. The library is larger and for the games that are Play Anywhere, I can continue my save file on my PC when my living room TV is unavailable.

I really think that Microsoft has a winning strategy with Game Pass this generation and it really surprised me how my attitude to the Xbox ecosystem changed this year. While I think both Sony and Nintendo have great exclusives, the value proposition for me of convenience and a rotating slate of quality games will likely keep me invested and subscribed, moreso than Xbox Gold or PS+ have in the past.

Figured I'd start putting together a thread as the flood of announcements and articles start coming out from this year's BlizzCon.

The site, where you can pick which streaming "channel" to watch: https://blizzcon.com/

Full schedule: https://blizzcon.com/en-us/schedule

Opening ceremony: https://www.youtube.com/watch?v=XyApQc-ZmSA

Diablo IV

• Blizzard on Diablo 4's Rogue and how PvP works within the open world
• Diablo IV: What's Next: https://www.youtube.com/watch?v=CO3LQqpiBvQ

Diablo II: Resurrected

• Trailer: https://www.youtube.com/watch?v=DRP62MGOrUo
• Interview on Eurogamer: The big Diablo 2 Resurrected interview
• Some more details on Ars: Diablo II Resurrected tops BlizzCon announcement flurry
• Diablo II: Resurrected - Deep Dive: https://www.youtube.com/watch?v=D3dL7ZeIAsE

World of Warcraft

• World of Warcraft Classic will be extended to include first expansion The Burning Crusade this year, along with paid character cloning and boosts, and "pre-nerf" raid bosses.

Overwatch 2

• Behind the Scenes of Overwatch 2: https://www.youtube.com/watch?v=lRj-GotnNaQ