I noticed that this title is advertised as having a native resolution of 1024x640. While not an abnormal resolution (it is 16:10 at true 1K), it isn’t a standard resolution. Do I need to add 1024x640 as a custom resolution in my GPU control panel, or can it upscale to other 16:10 resolutions like 1280x800 or 1728x1080? I have a 1080p screen.
If you have "Scale on GPU" set in your Nvidia control panel, the game will properly upscale to your screen resolution and will introduce black bars if necessary to keep the aspect ratio.
There are no different selectable resolutions to upscale to. There is only windowed mode (1024x640) and fullscreen (scales to your desktop resolution).
Windowed and fullscreen is a standard in 99.99% of visual novels. Very few of them allow you to select other intermediate resolutions.