U2720Q, using with a MacBook Pro late 2012

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@JorgeGallo  Are you determining that the display is running at 1920x1080 by looking within macOS or by checking the status info within the onscreen interface built into the display?  If you haven't checked the latter, check there.  The reason I ask is that macOS might be treating the display as "1920x1080-equivalent", i.e. running it in Retina mode and giving you the workspace equivalent of 1920x1080 while running the display itself at 3840x2160.  Retina displays have double the pixel density of normal displays, so when macOS thinks it's working with a Retina display, it uses graphical assets that are twice as wide and twice as tall so that when using you use a Retina display, things are incredibly sharp rather than incredibly small.  So in that setup, the display will actually be running at 3840x2160, but you get the same amount of real estate that you would have with a 1920x1080 display -- which is why macOS can label it as "Looks like 1920x1080" or whatever they call that mode these days.  Running 3840x2160 with standard non-Retina assets on a 27" display would result in some pretty small text and graphical assets, so it's possible that macOS just isn't giving you that option.  If you want it anyway, applications like SwitchResX allow you to have more control over how your displays are run.

JorgeGallo, 

Thank you for reaching out to us, what you are reporting is a limitation from the Macbook Pro 2012, this model if I'm not mistakenly uses a thunderbolt / mini display port output and you are using an HDMI cable, therefore you will have some limitations. 

This monitor has been tested with USB-C standards and VESA display modes. 

You can check more in depth the compatibility specifications in this article:

Using a Dell UltraSharp USB-C Monitor with a Mac

Hope you can find this information helpful. 

Kind regards, 

Thank you so much @jphughan for your answer. Just one more question if I may. I saw you say 4K screens won't work well with a Mac Retina, but I have found that, among the four screens Apple proposes in his website, one of them (the cheapest one) is a 4K. Do you think it would be as bad as the U2720Q or it would work better?

@JorgeGallo  You mentioned four screens mentioned on Apple's website, but I didn't see a link to any particular webpage, so I'm not sure what you're referring to there.  But note that I did NOT say that 4K in general won't work well on a Mac.  I said a 27" 4K display won't work well on a Mac.  My post focused on the importance of considering pixel density, which is the relationship between resolution and display size.  Using 4K resolution on a 27" display results in a pixel density that falls in the middle of two target pixel densities that Apple designs for, which means it won't be a great fit for Apple's ecosystem because it doesn't fit either one.  That's why I specifically said in my earlier reply that you can either use 4K resolution at a smaller display size to raise your pixel density closer to something that Apple actually DOES design for, or use 4K at a LARGER display size to reduce your pixel density to a DIFFERENT standard that Apple designs for.  But you don't want to be stuck in the middle.

But looking at the response you just got from Federico above, somehow when writing my original replies I missed that your MacBook Pro is a late 2012 model.  That system won't run 4K resolution.  The Tech Specs page for that system on Apple's website here indicate that it only supports up to 2560x1600 resolution on external displays.  This is a limitation of the Intel HD Graphics 4000 GPU in that system.  4K support wasn't available on that GPU.  And 4K 60 Hz over HDMI didn't become available until HDMI 2.0, which didn't arrive on laptops until around 2018.  Some older systems could run 4K 60 Hz over Mini-DisplayPort or USB-C/Thunderbolt 3, but they still needed a GPU that could support that resolution, and yours doesn't.

@jphughan I was referring to this one: https://www.apple.com/shop/product/HMUA2VC/A/lg-ultrafine-4k-display 

Yes, @jphughan I indeed noticed the it was almost 24" as you mentioned earlier, so got it, I will look for something that size for a future Mac. My MacBook works really fine but, I guess it won't last for ever!

Many thanks again for your great help.

@JorgeGallo  I just realized what you might have been talking about when you mentioned the "four screens" on Apple's website.  Are you looking at their iMac systems?  If so, those are entire Mac systems built into a display, not just a display.  The cheapest iMac is actually 1920x1080, not 4K, at least in the US.  But yes, there are some iMac options with 4K displays -- but notice that the size of the display on those iMacs is only 21.5 inches.  Having 4K resolution on a smaller display results in a higher pixel density of 202 ppi.  That is within the 200-220 ppi range that Apple designs their Retina graphics to use, so 4K at that size works well.  But you're trying to use 4K on a much larger 27" display.  That is not going to be a good experience on a Mac.  If you look at the iMac models that use a 27" display, they are all using 5K resolution, not 4K.

But again, iMacs are entire Mac systems built into a display, not just displays.  The only standalone display that Apple currently makes is the Pro Display XDR, which is a 32" 6K display, and it's very expensive.

@JorgeGallo  Happy to help, although sorry I didn't have better news for you!