This method sometimes fails on Windows 10/11 builds from 2021 because of UAC restrictions. If the game crashes on startup, revert to Method 1.
The 2021 community fix was to use the "Classic Town View" mod, which replaces the 3D flythrough with the static, painted 2D backgrounds from Heroes 3 , which scale beautifully to any width. heroes 5 widescreen fix 2021
Note for modern users: This is largely obsolete now, as the HD Mod (below) automates this. This method sometimes fails on Windows 10/11 builds