UnknownUnknown
Another report mentioned alt-entering out and changing settings. This is not possible on Steam Deck and seems to softlock the device in a certain way.
As mentioned by the other reviewer, DirectX mode does not seem to work. The game needed to be placed into windowed mode (alt-enter). From there, I needed to change View -> Graphics -> OpenGL. The game started working as expected from there, and entering full screen (alt-enter again) worked as expected.
Major input lag using standard keyboard+mouse.
If I was not moving my cursor around in the background (not selecing the game), it ran at 30 fps. Moving the mouse around let the game run at 60
It does not work in DirectX mode, only OpenGL. When you first run the game, it displays an error message "3D device not found" (twice) and then a black screen. When the black screen comes up, press Alt-Enter to go into windowed mode. Then you can use the menu View->Graphics->OpenGL. It will display an error message, after which you should close the game. That's the end of the setup.
When you run the game again, you will still get the "3D device not found", but if you press Alt-Enter to go to full screen, it will work fine. If you want to play in windowed mode, you need to press Alt-Enter twice when you run the game to switch to full-screen and back because it doesn't work initially in windowed mode. This last step is why I gave it a silver rating and not gold. If you play in fullscreen mode then it is a gold rating.
