We tried a USB-C cable, a DisplayPort to USB-C cable, a Thunderbolt 3 dock, and an eGPU and weren't able to get the full 5120 x 1440 resolution. With an iMac Pro, though, we were able to run the display at full resolution over USB-C. It's probably also going to work well with the 2013 Mac Pro (or one of the new 2019 Mac Pro models, of course), but for Mac notebooks, we don't recommend it.
There have been other reports from Mac users who have also been unable to get the display to work at full resolution with their machines, while others have had no trouble at all, so it's not entirely clear what's going on.