Let's check on the theory of mine, TV screens do have a weird resolution:
Numbers like 1080p and 720p refer to a TV's screen resolution — the more pixels a screen has the more picture detail it can show. A 720p TV screen is 1280 pixels across by 720 pixels down, and when you multiply those numbers you get the total number of pixels, which is 921,600.
Which means the size doesn't matter, a 20 inch screen has the same resolution as a 40 inch screen: either 1080p or 720p
I would like you to open Geomod's CFG file and change the following lines:
Before:
#windowed = 1
#borderless_window = 1
#campaign_resolution = 1920 1080
After:
windowed = 1
borderless_window = 1
campaign_resolution = 1280 720
Save and start Geomod. If possible make a screenshot, else describe to what extent the game's surface is displayed on your screen. If there is an error about the resolution figures then use 1024 768 instead.
Basic thought: this is the approximate TV resolution. Using windowed mode should display in a window that size, giving us an idea what resolution the TV is actually using, regular mode is supposed to stretch the designated resolution to the monitor's size which does not seem to work. The thought occurred to me keeping the age of the game in mind: in 1996 in nearly all cases you needed a special adapter to use a TV as a display for a computer.