Use the joystick/nub thing to navigate to the General menu in the display and switch DisplayPort Version from 1.4 (default) to 1.2.
Also pro tip if you're a photographer: switch the Picture Mode to DCI-P3 color mode, then within MacOS, go to Color Profiles, and instead of the default color mode (it's sRGB!), select the Display P3 color profile. At that point, the LG 34WK95U will look almost indistinguishable from your MacBook's display, which is using the Display P3 color profile by default.
You may be able to get black levels a bit more accurate if you use Spyder 4 or something to calibrate, but the default DCI-P3 mode is very very close already.