Same problem.
Everything seemed OK with de demo "bar" on the top right telling me I had 47h left, but I couldn't use the mouse (the pointer appeared on screen but did not interact with the buttons and clicking did not give results neither )
Kind of frustraded, I used a Steam Card (adding money to my wallet ) to purchase the game (canyon), making sure I deleted the demo before installing the actual game. I launched the launcher of the game in the steam app then launched the game.
Same. Results.
So I went to the Steam app again and instead of opening the launcher of the game, I launched the game itself.
Again, I couldn't use the mouse.

So here I am, having spent 20 euros for no reason and wanting your help
Sorry for any bad english, I am french.