Steam Deck and handhelds
The store page confirms keyboard-only play but does not promise controller support or a Steam Deck compatibility rating. A small download is not the same as verified handheld compatibility.
Demo requirements
The Demo lists the same Windows 10, 4 GB RAM, processor, graphics, and 300 MB minimum. It also lists a mouse-only option and play-at-your-own-pace support.
For input details, read the Click the Button controls guide. To compare the two Steam apps, see Click the Button Demo vs full game.