Compatibility Report

• Name of the game with compatibility issues: Arthurian Legends Demo
• Steam AppID of the game: 776240 (demo of full game 658890)

System Information

• GPU: AMD RX 5700
• Driver/LLVM version: Mesa 23.1.3
• Kernel version: 6.4.4-200.fc38.x86_64
• Proton version: proton-8.0-3c
  system_info.txt

Symptoms

Game fails to launch with recent Proton versions, first time launch there is pop-up window prompting to reboot. Subsequent launches nothing happens, Steam just says running for a while.

With older Proton version proton-5.0-10b the game launches without issue, there is no pop-up window prompting to reboot on first launch either.

Tested with:
experimental-bleeding-edge-8.0 - FAIL
proton-8.0-3c - FAIL
proton-7.0-6-rc5 - FAIL
proton-5.13-6d - FAIL
proton-5.0-10b - SUCCESS

Reproduction

• Launch game for first time with a recent Proton version (make sure there is no exiting compatdata folder)
• On first time launch you get this pop-up window saying "a reboot is required to finish the installation"
  
• Hit yes or No (makes no difference) nothing happens, game stops running
  steam-776240-experimental-bleeding-edge-8.0-1st-launch.log
  steam-776240-proton-8.0-3c-1st-launch.log
• Launch the game again, nothing happens, game stops running
  steam-776240-experimental-bleeding-edge-8.0-2nd-launch.log
  steam-776240-proton-8.0-3c-2nd-launch.log

Including also log of successfully launching the game on first attempt with 5.0-10:
steam-776240-proton-5.0-10b-success.log

I discovered that you can launch the game once with Proton 5.0-10, and then switch to Proton 8.0-3 and the game continues working. I guess there is a pre-requisite that fails to install on first launch with the recent Proton versons.

Note that I tested the Demo of the game, but the full game AppID 658890 allegedly has the same problem.