Hello @someg33zer, for the Big Picture mode half of this issue report, this issue is already being tracked at #8280.
For the Civilization IV side, we're tracking issues with games run with Proton in the Proton issue tracker. Additionally, we're using one issue report per unofficially supported game title. Feel free to add your experience with the game to https://github.com/ValveSoftware/Proton/issues/1973.
Closing in favor of the older issue reports.
Your system information
Please describe your issue in as much detail as possible:
From Big Picture Mode (BPM), tried to run Civilization IV with Proton. Got two error message dialog boxes show up complaining about XML issues, then the BPM interface comes back but it's like a non-fullscreen window over the desktop:
The same happens from the non-BPM Steam interface with the same dialog boxes but the Steam interface windows are fine.
Steps for reproducing this issue: