2688 x 1892 is the native screen resolution of the 8.3″ Surface Duo 2 when unfolded. Unlike the rest of the family, it has a weird tall 672:473 or 18:12.6 or 18:12.669642857142855 aspect ratio display. It has a total of 5.08 million pixels with the same high 401 PPI pixel density as the original Surface Duo.
1344 x 1892 is the native screen resolution when the device is folded. The aspect ratio now becomes 336:473 or 9:12.6 or 9:12.669642857142855 or 9:13 (Microsoft suggested value) with the same 401 PPI pixel density.
You can learn more about screen information for all Surface devices from the Surface display comparison table we made here.