External display works on 30Hz

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?

I had the same issue for a long time. At first, 60Hz worked. Then something happened and I'd only get 30Hz on my 4K Lenovo ThinkVision 27".

I stumbled upon this article and simply went to Display settings and hit "Resolution: Default for display". Immediately the display switched to 60Hz. Then I could reapply my Scaled text size setting and 60Hz remained.

What an unsatisfying fix!

Try EasyRes app from the app store. One of my 4K monitors get 30Hz when I connect 2 4K monitors to my MacBook pro. The 2 monitors works fine together on Windows. Apple Support doesn't help. EasyRes fix the problem with 1 click.

Given that all hardwares are capable (monitor, computer/GPU, cable).

The Mac should automatically set itself to 60 Hz when available. Otherwise you can select 60 Hz from the drop-down titled "Refresh Rate".

In your screen shot that drop-down is greyed down, because it only has one option (30 Hz). This means that the Mac has not detected that the cable and monitor are cable of 60 Hz refresh rate.

As the monitor supports 60 Hz and your Mac does so as well, all points to the cable. Please try again with another cable, and make sure you buy a quality cable that supports bandwidth enough for 4k @ 60 Hz.