The LG Ultrawide Monitor in 5K resolution, the new LG 34WK95U-W, currently doesn’t run over a Thunderbolt 3 connection on a MacBook 2018.
Both devices are apparently so new that they don’t yet want to work together on a Thunderbolt basis. So it is currently not possible to run the latest MacBook Pro with the latest display. Older years of construction with Thunderbolt 3 ports are not affected.
We assume that it should work smoothly after a macOS update. If you are currently looking for a small workaround and simply want to connect the MacBook with a Thunderbolt 3 to DisplayPort cable (5K compatible), you will also be disappointed: A corresponding cable from Moshi doesn’t seem to work with the widescreen format (or the monitor’s firmware doesn’t want it). In any case: bring some patience until the monitor or macOS is updated.
