Same issue for me, Mesa 23.1.3, Linux 6.1.52-valve16-neptune-61, Steam Deck.
I've looked into logs with PROTON_LOG=1 and game logs and noticed it happens after compiling numerous shaders (presumeably shader precompilation starts here), but error happens after splash screen and intro videos.
Anything I can provide to help this issue along?
It's the same with the full version. RTX 4090 here.
Using latest Proton Experimental (currently bleeding-edge-9.0-117178-20240904) the demo and the full game no longer crashes for me, and I'm able to get into gameplay :tada:
(not sure if there are any issues later in the game, going to play through in the next few days)
I had the demo crash on both Proton 9.0-2 and Proton Experimental.
I have checked whether there are updates for my system available and I am up to date
System Information:
Distro: Artix
GPU: RX 7800 XT 16GB
Mesa Version: 24.2.2-arch1.1
LLVM Version: 18.1.8
Kernel Version: 6.10.9-artix1-2
Proton Version: 9.0-2
https://gist.github.com/Simmonz/37b9815520626b5422e193ec245f7ee3
proton experimentalx2 2024-09proton 9.0-2x1 2024-09proton 9.0-2ex1 2024-08PROTON_LOG=1x1 2024-08
Compatibility Report
System Information
I confirm:
Symptoms
Game crashes after the developer/title splash screen videos, just before the game loads to the main menu. This error message "Assertation failed!" pops up:

Reproduction
Launch the game, watch the splash screen videos, and observe that the game crashes after that.
steam-3105370-experimental-bleeding-edge-9.0.zip