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I just upgraded to macOS Sierra. In El Capitan, I could have my 4k monitor (Dell P2715Q) scale so it was the equivalent of a 2560x1440 monitor, but in Sierra it only lets me do 2k/4k resolutions now.

Anyone know of a fix?

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This is over displayport. – Edward Jiang Sep 21 at 1:38
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I'm so glad other people are having this issue. I use 2 of these same dell displays from a 13" retina and it's driving me nuts. I had one of them working at first but then it went away after about a half hour... enter image description here – Jared Christopher Sep 21 at 13:05
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Filed a bug report and referred your # @RichardHurt. My report # is 28405804 – Chris Sep 21 at 13:40
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I have a 4k monitor which on El Capitan gave me 5 preset options for resolution. If I boot up my Sierra laptop with the monitor connected to display port AND the lid on my laptop is OPEN, i get these 5 options. As soon as I close the lid the 4 option (from left to right) disappears. – juice Sep 23 at 4:32
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macOS Sierra Beta 2 should fix this problem. It fixed my resolution issue. – Mike Sep 29 at 14:20
up vote 2 down vote

Immediately I thought to recommend enabling HiDPI mode, which basically allows you to change the display to use half of the real pixel density without changing the resolution:

sudo defaults write /Library/Preferences/com.apple.windowserver.plist DisplayResolutionEnabled -bool true

but then I did the math and realized that you want 2/3 of your full resolution, not half.

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

^ This feature does not seem to be applicable in macOS Sierra anymore.

Third party apps such as 'QuickRes' and 'SwitchResX' don't resolve the issue. They only see the same resolutions that macOS sees.

For what it's worth, a reboot should fix it temporarily when you have your display plugged into your laptop. Once the screen sleeps though the issue returns.

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1  
Hm, thanks! Yeah, putting the monitor at 1080p (as shown in my screenshot) still runs it in HiDPI mode -- just not sure why it's not scaling to any other intermediate sizes. Apple used to allow me to do this without a 3rd party tool, so I assumed this is a bug... – Edward Jiang Aug 29 at 0:04
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I just ran into the same thing with the GM release. Took me by surprise - I'll be keeping an eye on switchresx compatibility. – egid Sep 11 at 5:33
    
SwitchResX does allow me to configure the display as 2560x1440 but it is not HiDPi enabled. So, while the size is correct everything is a bit fuzzy. :( – Richard Hurt Sep 23 at 18:08
    
I had to restart after running that command to get it work. – Henry Oct 12 at 17:41

protected by Community♦ Sep 21 at 13:55

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