Solution: Delete options.ini located in %USERPROFILE%\Zomboid\. Then relaunch. Set resolution to your monitor’s native before touching any other settings.
Build 40’s default resolution is 800x600. Before starting a game: project zomboid build 40 download new
Before you download, know what you are losing. The jump from Build 40 to Build 41 was the biggest leap in the game's history. Solution: Delete options
Build 41 introduced 3D zombies, 3D items, and complex lighting. Build 40 uses the old 2D sprite system. project zomboid build 40 download new