LG 4k display (27UK600) not recognized at proper resolutions after upgrade to Mac OS 10.14.6

Boot to your Recovery drive and run Disk Utility> First Aid on your drive, reboot.

If you upgraded via the Software Update mechanism, then try this,

https://support.apple.com/kb/DL2010?viewlocale=en_US&locale=en_US

it does not matter that you are already on 10.14.6 this won't do any harm but it will reset some system files and caches

and may help in resolving your problem. Once downloaded then double0click to install.

I updated using this method and my Sony 4k HDMI TV/ Monitor still shows all the Scaled options.

I have an LG Ultra HD (27UD59B) hooked up on my 2017 MacBook Air through its Thunderbolt 2 port. The only way to get it to use its native resolution was to connect a 4k mini display to display adapter and 4k HDMI cable.

Originally I've tried the normal mini display to display adapter which I've used to hook up my old full HD screen. With that I could only select 1920x1080 max.

It was the same story when connecting the screen to my 2014 Mac mini.

I've bought this screen after Mojave was released, so I have no experience with older versions of MacOS.

Edit:

Have you tried the option show low resolution modes? Because on my screen it shows up as a low resolution option. I've noted in your preferences it's unchecked.

I have the same problem with my LG Ultrawide 34UM95, which has native resolution 3440x1440. But OSX, after the update, show max resolution of 2560x1080 only, even with holding the Option key while clicking Scaled

I have the same issue and have also been on with several senior advisors who have escalated it to the engineering team. After a few days of no solution, I went to Best Buy and purchased the Insignia USB-C to HDMI adapter and it worked. This issue seems to be related to adapters that do more than just HDMI. For me, it is the Apple AV Adapter (HDMI, USB and USB-C). Still waiting on a resolution.

Running 10.5.1 Catalina on a MacBook Pro Mid-2018.

I bought a used LG UltraFine 4K display in great condition. Tried it at the seller's house and it worked fine at full retina resolution. Now I am trying it out after it sat around for about 10 days and I can't get the resolution to go above 1080p when using the "Default for display" setting. 1920 x 1080 is the maximum within the "Scaled" options.

System Profiler tells me the following...

LG UltraFine:

  Resolution: 1920 x 1080 (1080p FHD - Full High Definition)

  UI Looks like: 1920 x 1080

  Framebuffer Depth: 30-Bit Color (ARGB2101010)

  Display Serial Number: 610NTRL05806

  Main Display: Yes

  Mirror: Off

  Online: Yes

  Rotation: Supported

  Automatically Adjust Brightness: No

  Connection Type: DisplayPort

I am connected to the left upper Thunderbolt 3 port on the MacBook Pro with the original cable for the monitor. It is the only thing connected to the computer.

I also tried connecting the monitor my iPad Pro Mid-2019, the image displayed but also maxed out at 1080p

I've tried the "Option" key approach to no avail. All it gives me is a "Detect Displays" button.

Question... once you swapped from HDMI to DP and you popped it into 3840x2160, were you able to scale the size of your icons, etc? On HDMI, when I put it into 4k, all of those icons get super small and I can't scale it.

Try holding the Option key while clicking Scaled.

I have the exact same issue. with no 4k res option ager "option click".

FYI -- I found "Display Menu" in the App Store - it is a FREE app - FIXED my display issue -- HIGHLY recommend.

This worked for me!!! Thank you for posting!!

Same problem here with a LG 43". I can chosse "scaled" resolutions but the monitor itself is only recognized as a 27" model.

Seems like 10.14.7 is in order.