

Works perfectly
I had a save file on the demo version and it got deleted after the main game's install. Back it up in advance and you won't have the same problem.
I use experimental, haven't really tested any other version.
Everything is pretty small on the screen. It's playable as long as you hold the Steam Deck up in front of you (instead of down in your lap).
good
Installed, started playing. Runs as if it was native.
Runs flawlessly as if I was running it native.

Doesn't work on multi-monitor
No matter which monitor you select in the Unity launcher, it will launch in the leftmost monitor - while trapping the mouse in your main monitor.
Unplayable in that state.
works just as well as native

As other commenters before me said you need to run proton 5.13-1. Other than that it runs great!

Runs perfectly with proton-5.13-1.
Does NOT work at all with TKG builds 5.18 or 5.19, -GE builds 5.9-GE-X-ST, proton-5.0-9, proton-4.11-13, or any other builds I tried. Only proton-5.13-1.
Only short play time, but its working fine as far as i can tell, so far is interesting. Will update report if that changes.
Proton 5.13 used.
Running GTX950m with proprietary nvidia drivers - as i typically run mobility powersaving layers (using pvkrun / bumblebee / optirun). Steam hardware is not reporting this :)