U2720Q, MacBook Pro, 29Hz?

We can see on the U2720Q Operating system drop down that there are no Apple operating drivers. For Dell Technical Support to offer assistance, you need to test the U2720Q on a true Windows operating system PC. Read the sticky at the top of this Monitors Forum, "Does my Dell monitor have Apple support?".

You should also post the issue on the Apple Forum to get assistance from other Apple users.

Hi @DELL-Chris M 

so you're saying Apple computers are not officially supported by Dell, then you can't assure the Dell monitors work correctly? If so, I think you should put this very clear in the product page on your website, cause otherwise we assume that it's obviously that a monitor work on a Mac. Very very disappointing. 

Also I'm talking with someone of the Dell Care that said me:

The aspect ratio or the resolution will depend on the window or application that you are currently opening. As some applications may not run in 4K as they were no developed to run in those resolution. Depending on the system that you have connected to the monitor, the resolution will get automatically switch to one that will allow to run the application with no problems.

As for why it  only correctly works with the USB C to Display port, that's because this monitor works with dongles or adapters while using that port and is not going to perform correctly when using a USB C to USB C cable.

You can check this page under the tech specs for this monitor.

The part where it says: 1 x USB Type-C (Alternate Mode with Display Port 1.4, USB 3.1 upstream port, Power Delivery upto 90W*).

When we say that USB C to USB C is not recommended, that's because this type of port will not give you as much resolution as the Display port connectivity.

so, basically, USB-C Power Delivery port is useless because by design it doesn't work well... and remember you provide the cable in the box!

You confirm this?

@eldoradooo  I hate to say this (although I can't say I'm surprised), but Dell Cares is completely wrong in their answer.  This seems to happen a lot when they try to answer even moderately technical questions.  Applications do not cause the entire system to change its resolution or aspect ratio (except maybe games that run full screen), and the USB-C input is not necessarily expected to be connected using dongles.  The spec they quoted in the manual does not mean that the USB-C connection can only support video, power, and USB 3.x when using adapters/dongles for each of those things.  It can carry all of those things over a USB-C to USB-C cable.  And in fact the manual clearly shows an example of connecting the display to a system via a regular USB-C cable.

It is also absolutely possible to run 4K 60 Hz over regular USB-C even from a system that only supports DisplayPort HBR2 (DP 1.2) over USB-C, so long as you are not ALSO trying to carry USB 3.x at the same time on that cable.  The reason that matters is that when you set up a USB-C link to carry USB 3.x, that consumes two of the four high speed lanes within the cable, which cuts your available video bandwidth in half.  If you have a system that supports DisplayPort HBR3 (DP 1.3/1.4) over USB-C, then half of a full link is still enough to run 4K 60 Hz, but half of an HBR2 link is not.  That's why the U2720Q offers a "USB-C Prioritization" setting in its on-screen menu.  If you set it to High Resolution, then it allocates all lanes to video so that even an HBR2 system can run 4K 60 Hz over USB-C -- but then you only get USB 2.0 speeds from anything plugged into the display's USB ports, since USB-C connectors have pins dedicated to USB 2.0, which means carrying that doesn't affect display bandwidth.  If you choose High Data Speed, then the display will run USB 3.x over USB-C, but in that case you'll need an HBR3 system if you want to run 4K 60 Hz.  If you want 4K 60 Hz and USB 3.x from an HBR2 system, you need to run two separate cables, one for video and one for USB 3.x data.

All that said, I can't account for why your system is detecting a 5K display over USB-C and detecting a 4K display when using USB-C to DP while saying it's rendering an effective 1080p when you chose QHD.  Unfortunately I haven't experimented with Macs running 4K displays in a while, and I've never done it with USB-C displays.

Hi @jphughan 

thanks for your answer, I'm completely agreed with you. Also answers by Dell are very vague and unclear.

How can I know if I have HBR3?

Anyway I checked the monitor settings and "USB-C Prioritization" was already set to "High Resolution"...

I have notified the Displays Team and Marketing of the fact that none of us in Technical Support have any Apple product to test on nor have we received any training on Apple product. It will be up to them to procure such Apple hardware and to provide the training. None of us at Dell would know what HBR the Apple MacBook Pro supports which is why I recommended that you ask the Apple users on the Apple Forum.
 
jphughan is correct on the technical specifications of the monitor.

@eldoradooo  Not sure how to check HBR support on a Mac, but I believe it would be HBR3 on a 15” MBP, since to my knowledge they give the discrete GPU direct control of the display outputs in that model. One way to test would be to switch the display to High Data Speed. If you can still run 4K 60 Hz, that would mean you have HBR3, and then you’d also gain USB 3.x. But of course you should be able to get 4K 60 Hz even now, so the fact that you’re seeing strange behavior means I’m not sure what will happen by switching that setting. But it’s worth testing especially if you’d want USB 3.x over USB-C.

Unfortunately HBR support information is still difficult to find across the board. Dell’s documentation for their latest WD19 docking stations shows different display support tables depending on whether you’re using an HBR2 or HBR3 system, and the documentation for their displays addresses this, but the documentation and product pages for their actual SYSTEMS don’t indicate HBR support information.

@whyyyyy  in fairness, while I don't have a U2720Q in front of me, I'm going to guess that if I were to test it on a variety of PCs, it would be detected and used as a 4K 60 Hz display as intended.  I also realize that Macs work properly with other 4K 60 Hz displays.  So I suspect this will turn out to be an interoperability issue with the specific combination of this display and Mac systems, or possibly even just certain Mac systems.  In that case, it won't be immediately clear which product is "buggy", so it may be premature to blame the display here.  I realize that doesn't affect the end result in your situation, so this may not be the display for you since I assume you'd rather keep your Mac than this particular display, but don't simply dismiss the possibility that the bug may be on the Mac OS/firmware side.  Apple has issued updates to improve compatibility with certain displays before, after all.

I have this EXACT problem on my 2018 13" macbook pro.

The worst part is I played around with the monitor HDR settings in the OSD and for a brief period the monitor was working at 60hz and showed up in the system report as a 4k instead of 5k.

So I know the cable is good and the hardware is capable of working properly. From what I can gather the monitor is reporting itself incorrectly to the OS. I'm very disappointed with this buggy product. Will likely return it.

@whyyyyy same here, it's M2T101

I precise that the monitor works really well on all the other fronts, but this "bug" that not allow to use USB-C>USB-C cable on a Mac is really disappointing.

To me, now it's not clear how and what to test for understand what's the real problem and mostly if there's possibility to solve.

Thank you for posting this! It allowed me to change the refresh rate to 60hz. I confirmed via the monitor's OSD that it is working at 60.

I have a LAN adapter plugged into the monitor's USB port and I think it briefly dropped connection after doing this which hasn't happened before. It's been about 10 minutes and hasn't happened again so I'll update if I have any more trouble.

Also own macbook pro 2018 and switchresx in enabling 60hz. Please provide your findings since I am also interested in buying this monitor.

Great! can you come back in a couple of days to post your findings? really looking forward to buying this monitor