Hi, Update that I got the LG 34WK95U-W working at 3840x1620 with my 14" M1 Pro on macOS 12.4 Monterey.
Here's what steps I had to do:
1) Update monitor firmware using macOS OnScreen Control version 5.47 from this link. I had to do this to get it to be recognised as a 5120x2160 monitor at all. Without doing this it just thought it was a 3440x1440 ultrawide and wouldn't even that resolution at high DPI.
LG Software, Firmware, & Drivers Download: Optimize your LG devices by downloading the latest drivers and firmware updates. Keep your LG products up-to-date.
www.lg.com
2) Using the display menu on the monitor itself, change the Display Port version to 1.4. Again it wouldn't show up as a 5120x2160 monitor without doing this.
3) I didn't need to use SwitchResX or Better Dummy, 3840x1620 showed up natively in macOS. Either macOS has updated something, or maybe LG have in the latest firmware, or I just got really lucky.
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