As per the title, I'd like to run NwN windowed but for the life of me can't find any option in the game or the config tool that allows it, am I missing something obvious or is it fullscreen only?

You sir, have made my day :)

Is there a way to get borderless windowed? I have tried a lower resolution that my monitor and tried using borderless Gaming, no joy when I click on my other monitor, as the game minimizes

Windowed Borderless Gaming 2.1.0.1 google that and run it and bingo there ya go

Tried the borderless gaming. It is massively glitchy with NWN. if I set the resolution to 1920x1080 it is either forced fullscreen non-windowed or if I hit alt-enter it goes into roughly 640x480.

Borderless Gaming works if I set to 1 resulotion size down from the 1920x1080 but if I leave/enter a building or change zones the graphics gets all glitchy.

But at least I now have something to work with some of my older racing simulators.