Can't run external monitor at native resolution with Big Sur

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Can't run external monitor at native resolution with Big Sur

I have a new ultrawide monitor (LG 38WN95C-W) with a native resolution of 3840x1600 but I find that Big Sur (11.5.2) won't let me drive it at its native resolution. The "default for display" option scales the UI to a ridiculously large 1920x800 (as reported in the System Report) and all of the provided "Scaled" options result in similarly non-native scaled resolutions (reported as "UI looks like" 2560x1067, 3200x1333, etc.).

The best option I can find is to hold down the option key when selecting "Scaled" in the Displays panel so that I can pick the native resolution 3840x1600. This does display the UI at normal proportions ("looks like 3840x1600") but it does so with a huge, double virtual resolution of 7680x3200. This in turn causes problems with certain graphical apps (like Final Cut Pro and Capture One) and even appears to cause performance problems. Because the virtual resolution is so high, these apps will display images and video frames and half the expected size in their windows.

For example, an image which is about the same size as the native resolution of the screen will be displayed at half the size of the screen when viewed at 100%. On the other hand, if I take a screen capture of the screen, I'll get a 7680x3200 file and the smaller-than-expected image in the screenshot will be at its correct, expected resolution. The trouble of course is that the monitor can't actually display 7680x3200 so I can't see or work with the images or videos at their true resolution on screen. Frustrating!

Interestingly, Apple's Preview app seems to compensate for this double virtual resolution and shows the same images scaled up to the expected size for the screen. At the same time, Apple's own Final Cut Pro does not compensate for this higher virtual resolution. Displaying a video in the editing window at 100% results in a image displayed at half the expected size (as compared to the native screen resolution).

This higher virtual resolution thing seems to be intentional in Big Sur – it even happens with the MacBook Pro's built-in screen but not to the same degree: I get a virtual resolution of 3584x2240 with the native resolution of 3072x1920.

My question comes down to: how do I get macOS Big Sur to run my display at its native 3840x1600 resolution with the UI not scaled to a different resolution?? Also, why do I not see other people reporting this issue? Anybody else seeing this??

I have reported the issue to Apple several Big Sur versions ago but of course there's no response. I've also reported it to the Capture One team in the hopes they can get a response from Apple.

Here's a cropped and compressed screenshot showing the double virtual resolution (to get under the size limit for uploads):

MacBook Pro with Touch Bar

Posted on Sep 9, 2021 9:24 AM

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Answer 1

Top-ranking reply

Incredulocious Author

Level 1

22 points

Sep 16, 2021 9:59 AM in response to Incredulocious

Update: I've now found a way to get macOS Big Sur 11.5.2 to work at my monitor's native resolution of 3840x1600 and still get a high refresh rate and/or HDR support.

Temporarily switch the monitor to use DisplayPort 1.2 instead of 1.4 using the monitor's built-in menu options.
In the Displays system preferences panel, hold down option key while selecting "Scaled" and select the native resolution (3840x1600) from the previously hidden list of resolutions. The HDR and high refresh rates options will not be available at this point.
Switch the monitor back to DisplayPort 1.4. HDR and high refresh rates are now available again and can be chosen. (Click the "Show low resolution modes" checkbox in the Displays system panel to reveal the "Refresh Rate" option.)

The display will now be at its native 3840x1600 resolution with no double virtual resolution (as shown in the system report or via screenshots). The "Default for display" option in the Displays system preferences panel still won't correctly recognize the display's native resolution – it will still choose a very low resolution of 1920x800 – so just leave things using the "Scaled" option with the true native resolution selected.

This fix (temporarily switching to DisplayPort 1.2 and then back to 1.4) holds across sleep/wake cycles and even across reboots for my 2019 MacBook Pro 16" and my LG 38WN95C-W ultrawide monitor. There's no need to repeat the process unless you choose "Default for display" again.

Because there's no double virtual resolution (7680x3200) any more, apps like Capture One and Final Cut Pro once again display images at their proper size in their windows.

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Answer 2

Sep 9, 2021 9:34 AM in response to Incredulocious

I forgot to add that there is one way I found to get my native resolution (3840x1600) without UI scaling and that is to change the LG monitor's settings to use DisplayPort 1.2 instead of 1.4. This eliminates the double virtual resolution that causes problems with apps like Capture One or Final Cut Pro, but it also limits the max refresh rate to 75 Hz instead of the 120 or 144 Hz that the monitor is capable of. This also disables HDR support.

So, there's a workaround, but it's not ideal. Also, this doesn't help address the same problem with the MacBook Pro's built-in display.

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Answer 3

Sep 9, 2021 9:49 AM in response to dialabrain

dialabrain wrote:

You could try SwitchResX. There is a 10 day free trial.

https://www.madrau.com/

Just downloaded it, tried it, same effect. Choosing 3840x1600 at any refresh rate (144Hz, 120Hz, 75Hz) via SwitchResX still causes macOS Big Sur to set up a virtual resolution of 7680x3200.

Seems like my workaround of using DisplayPort 1.2 (and giving up HDR and high refresh rates) is the best workaround for now.

Thanks anyway. Cheers!

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