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In addition to everything everyone else has said, the launch option: PROTON_LOG=1 %command%
(from the wiki). It will create a steam-<gameid>.log
in your homedir which can have lots of good wine/proton specific information in it.
You can also rename the user-settings.sample.py file in a given proton version in $HOME/.steam/root/steamapps/common/Proton - <version>/
to user-settings.py
and uncomment the additional wine debugging options (PROTON_LOG is already set in this file, but it is not active until it’s renamed or passed directly on the Launch Options line).
That Dirt 3 performance improvement though…
Might have to go dust off that game just to experience the speed