Yeah, but the article @JailhouseFrog shared is a guide on how to reduce the vertical pixels to achieve the 21:9 ratio. It’s literally turning off the vertical pixels so you would get Ultra wide feel.
You can’t add pixels horizontally without adding more monitor. And I think turning off the vertical pixels as was given in the guide is not taking your monitor to it’s full glory. Wasting the top and bottom part of the monitor as black bars instead of just zooming out while you still have vertical space that you can see.