Source code is now available on GitHub https://github.com/beemfx/DumbInfernal. As part of that process some updates were made to the game. PhysX was removed. The font was updated. The landscape texture was updated to use simpler geometry.
Source Code Released Update
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 21084316 · public branch
Steam updated · First observed