S3422DWG, 2560x1080 resolution?

What we see on pages 18 to 25 are the tested/validated resolutions. It appears that 1920x1080 is your only option for 1080p. To what other 1440p monitors are you comparing?

@AverageDad  Many GPUs can now do post-render downscaling specifically to deal with displays that might not have hardware support for your desired resolution.  If you go to Windows Display Setting > Advanced graphics settings, you'll notice that there are separate lines for desktop resolution and "active signal resolution".  It is possible to have your GPU render at 1080p and then just upscale that rendered image to the native resolution of the display.  In that setup, the rendering work is only "1080p-level", but the signal actually on the wire between the laptop and display will be at the display's native resolution, so that there's on dependency on any scaling capabilities of the display itself.  When the two resolutions involved in this setup do not share a common aspect ratio, GPUs typically have options as to whether the scaling should fit the entire display (creates distortion or cropping) or should be scaled proportionally (creates black bars).  You should be able to find options along these lines in the control panel application for your GPU, e.g. Intel Graphics Command Center, NVIDIA Control Panel, etc.

I was comparing to the Dell S3422DW monitor which is also a native 3440 x 1440 native resolution. That online user's manual states under 'preset display modes' that it supports 2560 x 1080 resolution at both 60 and 100 Hz. That's why I was surprised the S3422DWG doesn't list that as a supported resolution.

Thank you - I will check my adapter settings to see if I have this option. My graphics card is a Radeon HD7850 - not exactly state-of-the-art - which is why I'm trying to anticipate issues if I purchase the S3422DWG.