An earlier version of my build script ran on a build matrix including macos-latest and win32-latest, which I assumed was the only way to build for each platform, until I read the Electron Packager docs more closely. Turns out you can build for every platform from Ubuntu as long as you install Wine. This allowed me to simplify and speed up my action, and fully rely on game-ci/steam-deploy rather than writing my own platform-specific scripts for running steamcmd. Getting the Wine install instructions just right took a few iterations, but the command in the workflow file above has been working reliably.