MacOS 10.15 Catalina and LG 34WK95U-W not working at 5K

I've seen other people complaining (on LGs forums) about compatibility issues between the 2017 MacBook Pro Radeon 560 and the LG 34WK95U-W 5K monitor, being unable to output 5K (5120x2160) natively. We were told by LG support that the issue would be '..fixed with the next version of macOS..'. Well Catalina was released today and I excitedly updated to discover.... it's still not working. Is there anything else I should try? It's very frustrating to not be able to get the best experience out of this hardware combo, after purchasing these pairing specifically.

I've tried a completely clean install of 10.15 this morning and a PRAM reset - both to no effect. As you can see from the system report output below, the highest recognized resolution of this display is 3440x1440. The issue is the same with the laptop display closed or open. If I set the display to split screen (this monitor has a screen split function to display two separate inputs side by side - either 50/50 or appox. 80/20 split), the display works at 3840x2160 and is significantly crisper. I’m using the ThunderBolt cable that shipped with this monitor. Appreciate any advice!

  Model Name: MacBook Pro

  Model Identifier: MacBookPro14,3

  Processor Name: Quad-Core Intel Core i7

  Processor Speed: 2.9 GHz

  Number of Processors: 1

  Total Number of Cores: 4

  L2 Cache (per Core): 256 KB

  L3 Cache: 8 MB

  Hyper-Threading Technology: Enabled

  Memory: 16 GB

  Boot ROM Version: 202.0.0.0.0

  SMC Version (system): 2.45f1

 Chipset Model: Intel HD Graphics 630

  Type: GPU

  Bus: Built-In

  VRAM (Dynamic, Max): 1536 MB

  Vendor: Intel

  Device ID: 0x591b

  Revision ID: 0x0004

  Automatic Graphics Switching: Supported

  gMux Version: 4.0.29 [3.2.8]

  Metal: Supported, feature set macOS GPUFamily2 v1

Chipset Model: Radeon Pro 560

  Type: GPU

  Bus: PCIe

  PCIe Lane Width: x8

  VRAM (Total): 4 GB

  Vendor: AMD (0x1002)

  Device ID: 0x67ef

  Revision ID: 0x00c0

  ROM Revision: 113-C980AJ-927

  VBIOS Version: 113-C9801AU-A02

  EFI Driver Version: 01.A0.927

  Automatic Graphics Switching: Supported

  gMux Version: 4.0.29 [3.2.8]

  Metal: Supported, feature set macOS GPUFamily2 v1

  Displays:

LG HDR 5K:

  Resolution: 3440 x 1440 (UWQHD - Ultra-Wide Quad HD)

  UI Looks like: 3440 x 1440 @ 60 Hz

  Framebuffer Depth: 30-Bit Color (ARGB2101010)

  Main Display: Yes

  Mirror: Off

  Online: Yes

  Rotation: Supported

  Automatically Adjust Brightness: No

  Connection Type: DisplayPort