You'll probably have better luck looking for answers in the forum for that game. https://www.gog.com/forum/star_wars_knights_of_the_old_republic_series

Weird, because PC Gaming Wiki actually lists the game running in windowed as something you need a "hack" to do: [url=https://www.pcgamingwiki.com/wiki/Star_Wars:_Knights_of_the_Old_Republic]https://www.pcgamingwiki.com/wiki/Star_Wars:_Knights_of_the_Old_Republic[/url]

Anyway, check that site and see if anything looks like it can help. Also make sure you're not running it at a low resolution with your GPU set to maintain that. There are also some fan patches on that Wiki that might fix it. PC games require a little investigation sometimes. ;)

I'd recommend checking out Flawless Widescreen. It's quite finnicky but it's the only way that I know of to run it fullscreen at modern resolutions.

sounds like you don't have a Gpu or just arn't using it i.e, a very small screen an inch or two wide = no Vram

Use borderless gaming.