The Steam client preview/beta release on October 7 adjusted the launch method on Linux: when users add Windows executables as non-Steam games to their library, the client will now run them through Proton by default. Previously, users typically had to manually select Proton in the project's properties page; skipping this step could prevent the program from launching.
Proton is a compatibility layer built by Valve based on Wine, used to run Windows games on Linux. Steam has previously used it for supported Windows games in its store, and this update expands its default usage to user-added applications. Users can still change the compatibility tool being used.
This change is expected to streamline the process of adding games on Steam Deck and other SteamOS devices, including Windows games from other stores or standalone installers. The concurrent update also fixes two non-Steam game issues: games potentially failing to launch after modifying the target executable via the "Browse" button, and Steam's "Stop" button possibly failing to properly close games launched through external tools.
Additionally, the update adds an option to disable the screensaver during gameplay, corrects playtime display, and fixes controller ordering and Steam Input firmware issues on Linux. These changes are currently part of the preview/beta channel updates; whether the standard client receives the same behavior will depend on future stable releases.