Having problems and thinking that Diablo 4 is compatible with the Steam Deck? Then, you must read this article and know every detail at that point:
Diablo 4 is Steam Deck-compatible but not storefront-available. Manual installation via the Battle.net app is required.
How to do that
Switch to desktop mode, open the online browser, download and install the program, register for Battle.net, and buy Diablo 4.
Open the Steam app, click “Games” and “Add a Non-Steam Game” after installation.
Choose Battle.net and click “Add Selected Programs”. Your Steam library will include Diablo 4.
Diablo 4 plays nicely on Steam Deck, although several settings must be modified for a constant frame rate. Set the resolution to 1280×800 or below, the graphics preset to “Low” or “Medium”, deactivate anti-aliasing and other graphical effects, and the frame rate to 30 or 40 FPS for optimal performance.
Diablo 4 is easy to install and performs well on low settings, making it ideal for Steam Deck play.