2018 MacBook Pro + LG 4k display = no 60hz
On my Philips 328P6V monitor, using a USB-C to DisplayPort cable with my MacBook Pro (15 inch model from 2019 with Radeon Pro 560X), I first was stuck at 4k@30Hz and couldn't get 4k@60Hz (even though the cable supports it). I had to do two things:


Enable DisplayPort version 1.2 in the monitor's menu.
Choose "Resolution: Default for display" in my Mac's System Preferences/Displays.


The first point is pretty obvious, given that DisplayPort 1.1 only supports 30Hz for 4k.

The second point, however, is a bit weird. The original setting was:



And this setting delivered 4k@30Hz. Choosing "Default for display" changed it to 60Hz. After that, even re-selecting "Scaled" keeps my monitor at 4k60Hz.

What I believe might have happened is, that when I had first connected the display, it was still set to DisplayPort 1.1, and I assume my Mac remembered this. Resetting SMC/PRAM didn't seem to help. Switching the Resolution selector in the System Preferences probably made macOS rescan the connection and remember the updated DisplayPort 1.2 capability.