This is the way i managed to get this game working on Windows10 Systems. With this game having very weird collection of issues that only some users face, this may or may not work for you. Some users have said they had no issues playing this game on windows 10, so you may not even have to do anything at all. This is just what i had to do to play it in proper resolution, fullscreen and all that stuff.

You are doing everything described in this guide at your own risk of course, and there is no guarantee it's going to work.

-Go to game files and find the game exe file (should be named COI)
-Right click on the game exe file and click properties
-Now find a setting called "change dpi settings" and now check the box for "Override high DPI scaling behavior"
-There is a drop down menu for "scaling performed by" in the same place, make sure it's set to "Application"

After that the game might be running at low resolution. Just go to settings and choose your desired resolution. The game might crash or stop responding at this point. If that happens just close it and restart and now it should work on your desired resolution. I have tried both 1080p and 4k. They both work, but the game always crashes once when i have just changed the resolution.

I've tried this method on two different systems, both running different hardware and different versions of win10 and it has worked for both.

Hope this helps!