I have started debugging the game and could reproduce the issue with the Experimental version leading to crash on start (which I hope to fix soon). I am not completely sure if that is the same issue you are hitting though, this error from your log before the crash is suspicious:
"629.318:0100:0104:fixme:file:errno_to_status Converting errno 38 to STATUS_UNSUCCESSFUL".
The game worked for me out of the box with stable Proton 6.3-5. If it doesn't start for you this way, can you please try that with standard distribution kernel? Kernel version: 5.13.0-pf2+ suggests you have a custom built one.
The issue which I could reproduce with Experimental back then should be fixed in the latest Experimental update.
The latest Proton Experimental as of this post and Proton-6.13-GE-1 both work now for me with Stalker SoC.
Thanks fore retesting @shoober420, closing.
proton 6.13-ge-1x1 2021-07proton experimentalx1 2021-07proton 6.3-5x1 2021-07
System Information
The game crashes on launch.