So did I for the past week, but try this, it worked for me:
1. Go to: \SteamLibrary\SteamApps\common\Thief\Binaries 2. RENAME the "Win64" folder to whatever you want e.g. "Win64Backup" 3. COPY the "Win32" folder, so it should be "Win32 - Copy" 4. RENAME the "Win32 - Copy" folder to "Win64"
I just tried this a couple hours ago & now I'm finally playing the game, hope it helps you out too