VCMI mod files for high resolution reuploaded to git.
If you are stuck with the 800x600 resolution when you start VCMI, close VCMI, download the files and directories “bonusIcons” and “extraResolutions” repertories. Unzip, and place them in XXX (Windows), YYY (Android), ZZZ (Mac) or ~/.local/share/vcmi/Mods (Linux). Then start any scenario, open System Options dialog and voilà, other resolutions than 800x600 are availables.
Note that you need to restart VCMI for the change to take effect.