@henrys I got it working! Everything is looking crisp at 3840x1620 on my LG 34BK95U-W ultrawide, powered by my M1 Air ?
My setup:
- M1 MacBook Air
- macOS 12.3.1
- LG 34BK95U-W
- Interface: Thunderbolt 3 cable (using either DP 1.2 or 1.4—doesn't matter)
- Resolutions available to me: 3840x1620, 3414x1440, etc.
Basically what you need to do is this:
- Install BetterDummy
- Create a Dummy (i.e. a virtual display) with a "Custom Aspect Ratio" of whatever resolution you want (e.g. 3840x1620)
- Set that Dummy's "Mirroring Target" to your LG 5K (i.e. mirror the virtual display to your actual display)
And voilà, you have your LG 5K running at whatever resolution you picked ? I've gotta say, running an ultrawide at HiDPI is incredible for productivity. I had previously purchased a Studio Display and, while nice, I returned it after 2 weeks because what I really wanted was more screen real-estate. That's when I bought the LG.
FYI, I tried
SwitchResX, and it didn't help. What I learned is that SwitchResX essentially makes it easy for you to set custom resolutions for your external display, leveraging functionality to do so already built into the underpinnings of macOS. However, on Apple Silicon, Apple seems to have stopped supporting custom resolutions for external displays in macOS, so SwitchResX can't help you (see note
here: "
it's not possible to create custom timings on M1 Macs because this function was completely removed by Apple in the implementation of the new graphical subsystem").
The reason BetterDummy works is that macOS on Apple Silicon seems to support almost any resolution on an external display
if the external display is mirroring another display using that resolution. So if you followed the instructions above, macOS thinks you have a 3840x1620 HiDPI monitor connected to your mac, and you're simply mirroring its contents to your LG 5K. Super odd that this hack works, but it does.
And since you were curious, the reason the "Export EDID" button in SwitchResX was grayed it out for you is that this button, I believe, leverages functionality in macOS to read your external monitor's EDID information, but this function doesn't exist for external displays on Apple Silicon macs (again, see
the same note from the SwitchResX FAQ: "
export the EDID if the display does support it… I've never seen it supported on the M1 Macs"). If you Google for exporting EDID on macOS, you'll probably run into posts telling you to run
ioreg
in your Terminal. This gives you your monitor's EDID info on an Intel mac, but not on Apple Silicon.
Finally, the world is your oyster with BetterDummy. I know you wanted 3840x1620, but you can really create your Dummy at any resolution you want. As long as both the horizontal and vertical resolution you specify are an even number, you'll get a nice, HiDPI image when you mirror the Dummy to your monitor (choosing an odd-numbered resolution like 3841x1621 for your Dummy will result in a non-HiDPI, aka everything-is-tiny, image when mirrored). To make it easier for you, here are some resolutions I've tried which seem to look great:
- 4010x1692 (my favorite)
- 3414x1440
- 3360x1418
Finally, it's been mentioned before, but pro tip: install
Monitor Control, so you can control your LG's brightness and volume directly from your keyboard ?
Hope this helps! The ultrawide at HiDPI really is a beautiful thing ?