The Talos Principal 2 demo is available in Steam now, the full game comes out in November.
https://store.steampowered.com/app/835960/The_Talos_Principle_2/
But since the games is officially Windows only, it won’t let me download/install the demo (because linux).
Why Steam?!?? You’re going to let me use Proton to play the full game sp why not allow the demo to run the same way?
If anyone knows a work-around I’d be very happy.
EDIT: The suggestion by @ECCTM worked very well and I’ve started playing the demo. It “just worked”.
SECOND EDIT: I started a new Community for discussing the whole Talos Principle series, for anyone interested.
You must already have the setting enabled (as do I). But on a new install of Steam, only games that have been approved by Valve will run. And that’s using the old system, and not the new system that the Deck uses. So there’s is only a small amount of games supported.