So, I made a guide on steam on this subject but I figured I could post it here as well. So if you really want borderless fullscreen to work as expected give it a try and let me know if it works.
How to make Borderless work as you'd expect
To start off with, exit the game. Then you need to locate "settings.tml" in your "Documents folder -> Neverwinter Nights(scroll down to the bottom)"
With "settings.tml" opened in notepad you need to find the section called "[graphics.window]"(usually found around line 184) and copy the section below which aligns with your desktop resolution.
For 1080p
[graphics.window]
mode = "windowed"
[graphics.window.fullscreen]
height = 1080
toggle-to-borderless = true
width = 1920
[graphics.window.windowed]
borderless = true
height = 1080
width = 1920
[graphics.window.windowed.position]
mode = "remember"
x = 0
y = 0
For 1440p
[graphics.window]
mode = "windowed"
[graphics.window.fullscreen]
height = 1440
toggle-to-borderless = true
width = 2560
[graphics.window.windowed]
borderless = true
height = 1440
width = 2560
[graphics.window.windowed.position]
mode = "remember"
x = 0
y = 0
For 4k
[graphics.window]
mode = "windowed"
[graphics.window.fullscreen]
height = 2160
toggle-to-borderless = true
width = 3840
[graphics.window.windowed]
borderless = true
height = 2160
width = 3840
[graphics.window.windowed.position]
mode = "remember"
x = 0
y = 0
If that doesn't do the trick there might be another step needed, depends on how your scaling works.
For the second step locate "Nwnmain.exe" and right click it; Properties -> Compatibility -> Change high DPI settings -> Override high DPI scaling behaviour -> System.
Problems and Questions
"My settings in settings.tml are not being stored."
Right click it and make sure it's not set to Read-only.
"I can't find nwnmain.exe."
Right click "Neverwinter Nights" in your steam library and choose properties -> Local Files -> Browse Local Files. The file will be in "bin" -> "win32"
"The game isn't scaled to my screen even with those changes"
This is most likely an issue with your desktop scaling which you'll find by right-clicking your desktop and choosing Display Settings. If "Scale" is set to anything higher than 100% you'll need to either set it to 100% or make a few adjustments in the "settings.tml" like the example below.
For example; If your "Scale" is set to 125% while your resolution is 1920x1080 you could use something like this:
[graphics.window]
mode = "windowed"
[graphics.window.fullscreen]
height = 1080
toggle-to-borderless = true
width = 1920
[graphics.window.windowed]
borderless = true
height = 869
width = 1537
[graphics.window.windowed.position]
mode = "remember"
x = 0
y = 0
Link to steam guide
https://steamcommunity.com/sharedfiles/ ... 3020080842