Please describe your issue in as much detail as possible:

It is not possible for multiple Linux user accounts to run games from a single shared steam library with proton due to a file permissions issue. It would be very valuable to fix this issue for those looking to share games on a single system (family sharing, etc.). Having multiple installations of the same game on a single system isn't an attractive solution due to the large size of many modern games.

This issue has been documented previously in https://github.com/ValveSoftware/Proton/issues/4820, https://github.com/ValveSoftware/steam-for-linux/issues/3942, and https://github.com/ValveSoftware/steam-for-linux/issues/6958

There is also a PR to address this issue here: https://github.com/ValveSoftware/Proton/pull/4861

Tagging some of the users from the above mentioned issues here:

@crlsgms @shelterx @Maykin-99 @geoffryan @Nomz420 @VannTen @Adam-Saeed @artrsnd @kisak-valve @dottgonzo @alexbarcelo @thepowersgang @EgorIII @kon14

Steps for reproducing this issue:

1. Install steam library games in a folder to be shared between multiple Linux users.
2. Grant Linux users file access to the shared folder.
3. Attempt to run a game from the shared folder using proton with the different Linux user accounts.

The resulting error looks like this:

wine(server): /opt/games/Steam/steamapps/compatdata/430190/pfx is not owned by you