So I just got my 34WK95U and very disappointed. It doesn't work! Suppose to be plug and play but when you plug it in the mac display just flashes on and off. It works when PBP is set to 2/3rds but only displays 2/3rds which is no good. It would appear the new Macbook Pro 2018 doesn't support this monitor after all, at least not yet. I'm running Mojave 10.14
Think I'll be returning this tomorrow.
It does work, just not yet with Thunderbolt. Use a USB-C to Displayport cable.