I have MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports) with macOS High Sierra installed. I plugged it in to external display: LG 24UD58 24" via DisplayPort through USB-C
For unknown reason Macbook works at 30Hz instead of 60Hz. I managed to achieve 60Hz once somehow by switching between resolutions in Display settings, but I couldn't reproduce this anymore :(
How to achieve 60Hz with external display on Mac?