Hi! The game is controlled with the mouse. There are some keyboard shortcuts but not enough to play the game. Why does the mouse not work? Is the cursor position wrong? Or does it not move at all?
On a hunch, could you try running the game from the terminal using
SDL_VIDEO_X11_DGAMOUSE=0 ./epicinium
from the directory that the binary named "epicinium" is in? If that fixes it, we can add that to the next version.