This happens on some systems because of Windows high DPI scaling, if display scaling is not set to 100%. The game has a script that should disable this behavior automatically, but currently it's not working in all cases. To fix this, you should do it manually.

Find the ArmoredBrigade.exe in the game folder and do it this:

In Explorer or on the Start menu, right-click the application name, select Properties, select the Compatibility tab, and then select the Disable display scaling on high DPI settings check box.

Note:
In Windows 10 Version 1703 and later version of Windows, the text of the Disable display scaling on high DPI settings option is changed to Override high DPI scaling behavior, scaling performed by: Application.

https://support.microsoft.com/fi-fi/help/3025083/windows-scaling-issues-for-high-dpi-devices

And the window is not fullscreen (I see the bottom of my office), what a badly programmed game.
I guess you'll ask me to deactivate my taskbar...
You still use Windows 95 tools to program games?

EDIT: It is not told: In Change Settings, do not set the resolution of Window size:
Tree lines under there is written DESKTOP SIZE, we have to click on it so it becomes yellow!, and it will later make the game fullscreen...

So, the player must not verify nor choose other than what the dev enforce. Nice.
I wonder why you made those option settings, if we must not touch them.
I always rush to the options in all games, so I sure not have to quit my ongoing game. I verify and prepare at first before beggining to play.
Your game is maybe the sole which made me a bad game, by you badly explained options.
At least, what is badly made is these options, how they are named, no talking about fullscreen!

As a patch, before 'desktop size', write "FULLSCREEN":

". FULLSCREEN: Desktop Size (Just click here yellow) "

and write it immediatly under Window option, not 3 lines later so we may think it's not related to actually choosing the display.

. WINDOW: (choose your size)
. FULLSCREEN: Desktop Size (Just click here yellow)

Or take some dev class about how to program good UI. Half a day should suffice, so we're able to understand what you made.