The scroll-down list is just entirely blank/black, and trying to set it manually via the .INI does not work...

Very annoying to have crappy graphics and two black bars taking up 1/4 of the screen.

If you Alt Enter into Window mode does it let you change the resolution?
If so, just Alt Enter back to Fullscreen and the settings will stick.
Failing that, what graphics card and operating system are you using?

Nope, the scroll-down list is still entirely void of content.

I'm on a Win10 gaming laptop with a GTX 970.

A lot of laptops have a 59hz refresh rate.
If yours is that, does your NWN2.ini show the right refresh rate?

My monitor features 75hz.

Uhm. Hello?

...help.

Have you installed DirectX 9.0c?
Don't use the web installer if you are on windows 10
Make a new temporary folder on your desktop.
Go here http://www.microsoft.com/en-us/download/details.aspx?id=8109 And download the June 2010 runtimes to the temporary folder .
Disable your antivirus software.
Then scroll down and run DXSETUP.exe (see pic)
When it says, Installation Complete, you can delete the temporary folder, and re-enable your antivirus software.

Failing that, ask GOG Support.

DirectX 9 install shouldn't be necessary. AFAICT old games at GoG that need it, install it.

I installed NWN1 on a clean Windows 10 install and it worked perfectly with no hitches at all.

The "Resolution List" should come from the OS, when it queries the monitor for what resolutions it supports.

If I go to "Nvidia Control Panel", and under "Display", select "Change Resolution", the list that I get to select from is identical to the list I get in NWN/NWN2.

I was start by checking that list to see if something has gone wrong with monitor reporting resolutions in NVidia Control Panel, and maybe try updating your NVidia drivers.

Except that it is installed as part of an automated process, so if your antivirus software stops the older .dll's from being registered (which often happens) then you get no warning.
If you try to install the old DirectX runtimes yourself from Microsoft and your antivirus stops it, it gives you an error message.

Third party AV cause more grief than benefit IMO, I just stick with MS options.

I was testing Win10 and installed a bunch of my GoG games and they all installed and worked, with no tweaks, extra installs at all.

GoG installs are quite good if you have a sane computer.

In this particular case, if you didn't have DX9, the game wouldn't run.

Windows 10 embedded DirectX is backwards compatible to DirectX 9.11, so it will run, but not properly as it needs the earlier 9.0C.
Whereas with Witcher 1 that uses the same engine, the installer checks for 9.0C and gives an error message if you haven't got it installed, NWN2 doesn't.
When I installed it and AVG blocked the DirectX registration I got no warning at the time.
The game ran, but with lots of problems and only checking for errors in event viewer at the time I installed it showed that 9.0c had been blocked.
I've since seen people using kaspersky and avast with the same problem.

Uninstall, disconnect from net, disable your third party AV, and reinstall game.

Or as I said before, get rid of third party AV, it really isn't worth the hassle.