Support for Steam Deck (and I assume Linux in general?) is broken with the latest update (20 January 2023). As of writing, you'll need to manually revert the game files to a previous version (31 July 2022) to run the game.

For reference: https://www.reddit.com/r/Steam/comments/611h5e/guide_how_to_download_older_versions_of_a_game_on/

0. Open the Steam properties for Thrill Penguin

   • under Compatibility, force "Proton Experimental"

   • under Updates, change frequency to "Only update this game when I launch it."

1. Switch to Desktop mode.

2. Open Konsole and run the command steam steam://open/console to enable the Steam console.

3. In the Steam console, run the command download_depot 1981480 1981481 3666778339076773055 to download the game files for the previous version. You won't see any indication of progress, but the location of the game files will be shown in the console when the download is complete.

4. Navigate to the installation directory for Thrill Penguin (one way is to open the Steam properties for the game, and then under "Installed Files," click "Browse").

5. Create a new folder called "_backup" (or something similar) in the installation directory

6. Move all of the downloaded game files from their location shown in the Steam console into the newly created "_backup" folder.

7. Manually delete all other files from the Thrill Penguin installation directory so that the "_backup" folder is the only thing in the directory.

8. Copy and paste the downloaded game files from the "_backup" folder into the top level of the Thrill Penguin installation directory.

At this point, the game should run without issue when launched through Steam. If the game updates on launch, switch back to Desktop mode and repeat steps 7 and 8. If you're still having issues, you might need to add the Thrill Penguin executable as a non-steam game in Desktop mode and then run it as a non-steam game after doing steps 7 and 8 (I did this, but I'm not sure if it's necessary), and then you should be able to remove the non-steam entry and boot the game normally after successfully running it once. FWIW, I haven't had any issues since I first got it to launch.