Since 2015, most LG computer monitors has a 4-way joystick instead of distinct buttons for power, menu, etc. This is much more convenient and intuitive, but exisiting shortcuts for the old OSD menu system no longer worked. One notable loss was a publicly known way to get to the factory service menu to tweak the monitor's colors, check panel model and firmware version, and access testing modes. Fortunately I found a manual documenting how to get to the service menu. It works on my 29UM67P ultrawide monitor and should work for most monitors with joysticks.
To get to the service menu, follow these steps:
The service menu operates like the normal menus, with up/down moving through the list and left/right changing the highlighted setting. Pressing in the joystick seems to dismiss the menu. There isn't much documentation on the settings so exercise caution and keep in mind you risk bricking your monitor. If you have any questions, I recommend starting a topic on a savvy forum such as BlurBusters.