To avoid the "squashed" look of a 4:3 image stretched to 16:9, use your graphics card settings to add black bars:
If you cannot get 16:9 to work without the image looking "squished," you can force your graphics card to maintain the original 4:3 aspect ratio with "black bars" on the sides. heroes 5 widescreen fix 2021
Disable Steam overlay for Heroes V (right-click game → Properties → uncheck "Enable Steam Overlay"). How to Play Heroes of Might and Magic
The 2021 widescreen fix uses a combination of custom code and modified game assets to enable seamless widescreen support. Key features include: heroes 5 widescreen fix 2021