How do I achieve 5120x1440 with my e5490 on my monitor C49RG90?

@Richard1938  the Latitude 5490 (not E5490; the E was dropped when the E-Port underside docking connector was dropped) can indeed run 5120x1440, at the normal 60 Hz refresh rate.  You don't need an discrete GPU at all.  The Intel GPU can support up to 4K resolution, and if you do the math, you'll notice that 4K is actually slightly more total pixels than 5120x1440 "dual QHD".  However, it appears that a bug in a recent Intel driver update broke 5120x1440, so you might have to force an older driver onto your system, unless maybe an even newer release has fixed this issue since I last addressed it.  This came up in this thread where an XPS 15 user was asking about running this very same display.  The XPS 15 has a discrete GPU, but the Intel GPU still has direct control of the display outputs, fyi.  I initially suggested some basic troubleshooting earlier in that thread because the person who posted was initially limited to a lower resolution, but the post marked as the solution is where I finally found a link to an Intel forum that talked about this issue and how to resolve it.

Anyhow, you'll want to use a USB-C to USB-C cable that supports video, or else a USB-C to DisplayPort cable.  They'll both allow you to run that resolution, although note that even if you use a native USB-C cable, you'll be limited to USB 2.0 speeds for anything you plug into the display's USB ports.