Your system information

• Steam client version (build number or date): May 7 2021, 23:55:52
• Distribution (e.g. Ubuntu): Arch Linux
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

Original Issue is raised in the Proton repository though it's been noted that this is more a Steam Client issue than a Proton issue: https://github.com/ValveSoftware/Proton/issues/4820

I've followed these instructions on Reddit to allow multiple Linux users to share the same installation folder without dealing with permission issues. That seems to work so far for Linux-native games.

The issue with Proton games is that Wine does not allow using a Wine-Prefix that doesn't belong to the current user.

Example:

Both Steam clients on both Linux accounts are configured to download the games in /opt/games/Steam.

User maykin installs a Windows game and a Wineprefix in /opt/games/Steam/steamapps/compatdata/430190/pfx is created.

User steamuser wants to play the same game.
It does not need to install the game again, since maykin already installed it.
When attempting to start the game nothing happens (no game & no error message).
When inspecting the logs the following error occur:

Installing breakpad exception handler for appid(steam)/version(1618256785)
Proton: Upgrading prefix from 5.13-1 to 6.3-2 (/opt/games/Steam/steamapps/compatdata/430190/)
Proton: Removing stale builtin /opt/games/Steam/steamapps/compatdata/430190/pfx//drive_c/windows/system32/amd_ags_x64.dll
Proton: Removing stale builtin /opt/games/Steam/steamapps/compatdata/430190/pfx//drive_c/windows/syswow64/amd_ags_x64.dll
wine: '/opt/games/Steam/steamapps/compatdata/430190/pfx' is not owned by you
wine: '/opt/games/Steam/steamapps/compatdata/430190/pfx' is not owned by you
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
wineserver: /opt/games/Steam/steamapps/compatdata/430190/pfx is not owned by you
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_64/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
ERROR: ld.so: object '/home/steamuser/.local/share/Steam/ubuntu12_64/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
wine: '/opt/games/Steam/steamapps/compatdata/430190/pfx' is not owned by you

The relevant part is (so I assume) wine(server): /opt/games/Steam/steamapps/compatdata/430190/pfx is not owned by you.

The directory is owned by maykin but steamuser has read and write access to it but Wine - for security reasons apparently - doesn't care and demands that the prefix is owned by the current user, i.e. steamuser.

My suggestion:

1. Create a new prefix per user:
   Instead of creating the prefix here: /opt/games/Steam/steamapps/compatdata/<gameid>/pfx we could place it there: /opt/games/Steam/steamapps/compatdata/<gameid>/pfx/<userid>
2. Use symbolic links so that all prefixes share the same data:
   Put the device_c in a separate directory outside the prefix, e.g. in /opt/games/Steam/steamapps/compatdata/<gameid>/data, and place a symbolic link in /opt/games/Steam/steamapps/compatdata/<gameid>/pfx/<userid/device_c that points to the data directory

Additionally I'd like to note that this is what a Wine moderator proposes to do: WineHQ Forums