Can't launch the demo on Steam Deck - any ideas why?

[farley2k]

When I try to launch it on the deck I get the message
"Steam client is not running or you don't own the game or the demo"
This happens from Gaming Mode or the desktop.
Any ideas of how to fix it?

[Arirukuto]

my problem is, the demo is starting, but after i bought the real game, the demo and the real game loading for infinity.