Your system information

• Steam client version (build number or date): 1791918634
• Distribution (e.g. Ubuntu): Arch rolling
• Opted into Steam client beta?: No
• Have you checked for system updates?: No
• Steam Logs: [generate by running this command in a terminal tar -zcvf ~/Desktop/steam-logs.tar.gz ~/.steam/steam/logs]

steam-logs.tar.gz

• GPU: Nvidia

Proton version: Proton experimental & GE-Proton & Etaash proton

1. Goto https://store.steampowered.com/app/3859210/Rhythm_Animal_Cafe/ and download the demo
2. Click Start game
3. It shows it's starting but then it goes back to "start game", silently. Nothing launches.

Console log when I click "Start game":

chdir "/mnt/nvmeexfat/SteamLibrary/steamapps/common/RhythmAnimalCafeDemo"
ERROR: ld.so: object '/home/bczhc/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/bczhc/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/bczhc/.local/share/Steam/ubuntu12_64/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
ERROR: ld.so: object '/home/bczhc/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/bczhc/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
Game Recording - would start recording game 3979510, but recording for this game is disabled
Adding process 473005 for gameID 3979510
Adding process 473006 for gameID 3979510
Adding process 473007 for gameID 3979510
i386-linux-gnu-capsule-capture-libs: warning: Dependencies of /usr/lib/mangohud/lib32/libMangoHud.so not found, ignoring: Missing dependencies: Could not find "libxkbcommon.so.0" in LD_LIBRARY_PATH "/opt/cuda/lib64:/opt/cuda/nvvm/lib64:/opt/intel/oneapi/compiler/latest/lib:/usr/lib32:/usr/lib/perf:/usr/lib/libfakeroot:/usr/lib:/mnt/nvmeexfat/SteamLibrary/steamapps/common/RhythmAnimalCafeDemo", ld.so.cache, DT_RUNPATH or fallback /lib/i386-linux-gnu:/usr/lib/i386-linux-gnu:/usr/i686-pc-linux-gnu/lib:/lib32:/usr/lib32:/lib:/usr/lib
Proton: Upgrading prefix from None to 11.0-100 (/mnt/nvmeexfat/SteamLibrary/steamapps/compatdata/3979510/)
Traceback (most recent call last):
  File "/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/proton", line 2204, in <module>
    g_session.init_session(sys.argv[1] != "runinprefix")
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/proton", line 2075, in init_session
    g_compatdata.setup_prefix()
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/proton", line 1002, in setup_prefix
    self.copy_pfx()
    ~~~~~~~~~~~~~^^
  File "/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/proton", line 887, in copy_pfx
    self.pfx_copy(src_file, dst_file)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/proton", line 864, in pfx_copy
    os.symlink(contents, dst)
    ~~~~~~~~~~^^^^^^^^^^^^^^^
PermissionError: [Errno 1] Operation not permitted: '/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/files/lib/wine/x86_64-windows/wordpad.exe' -> '/mnt/nvmeexfat/SteamLibrary/steamapps/compatdata/3979510/pfx/drive_c/Program Files/Windows NT/Accessories/wordpad.exe'
Adding process 473106 for gameID 3979510
Game Recording - game stopped [gameid=3979510]
Removing process 473106 for gameID 3979510
Removing process 473007 for gameID 3979510
Removing process 473006 for gameID 3979510
Removing process 473005 for gameID 3979510

Additional info

I'm able to manually launch it from the terminal:

❯ pwd
/mnt/nvmeexfat/SteamLibrary/steamapps/common/RhythmAnimalCafeDemo
/mnt/nvmee/St/s/common/RhythmAnimalCafeDemo ❯ MANGOHUD=1 PROTON_ENABLE_WAYLAND=1 STEAM_COMPAT_CLIENT_INSTALL_PATH=$HOME/.steam/steam STEAM_COMPAT_DATA_PATH=$HOME/protondata ~/.local/share/Steam/compatibilitytools.d/proton-EM-11.0-1-beta1-8-ga3f7ba52-x86_64/proton run ./GameLobby.exe 

Update

Oh wait. I solved this issue by moving the game into my ext4 filesystem. It originally is installed in my exfat filesystem and this log line:

PermissionError: [Errno 1] Operation not permitted: '/mnt/nvme/SteamLibrary/steamapps/common/Proton - Experimental/files/lib/wine/x86_64-windows/wordpad.exe' -> '/mnt/nvmeexfat/SteamLibrary/steamapps/compatdata/3979510/pfx/drive_c/Program Files/Windows NT/Accessories/wordpad.exe'

may suggest it performs linking operation on my exfat fs and it fails thus my game won't start right?

It will be better if Steam Linux can notify users even a little bit when encountering such issues, instead of failing silently.