Fails to launch by default due to hardcoded file paths in DISCIPLE.ini. Resolved by creating symlink to game folder and placing it in

(steam library location)/steamapps/compatdata/281450/pfx/drive_c/Program Files (x86)/Steam/steamapps/common/Disciples Sacred Lands Gold

"Disciples Sacred Lands Gold" being the symlink itself. Runs perfectly after this on both Proton 9.0-3 and the current experimental version.