MacBook Pro M3 can't connect to DELL U3214Q monitor with 4K60Hz

Dell UP3214Q – Documentation

The manual indicates that this is a 34" monitor with Mini DisplayPort and HDMI inputs. Page 10 of the user manual says that the maximum resolution is

• 3840x2160 at 60 Hz (DisplayPort 1.2)
• 3840x2160 at 30 Hz (HDMI)

Since you are using the DisplayPort input, and the Mac should be capable of supporting 4K @ 60Hz, my suspicions would fall upon the adapter cable.

What did the description of your USB-C to Mini DisplayPort adapter cable say with regards to the highest resolution and refresh rate that it supports? On Amazon, there are many adapter cables whose description claims support for 4K@60Hz, but I found at least "4K" one whose product page said it was limited to "4K*2K 30 Hz."

at those ferocious data rates, your adapter.cable length should be ONE meter or shorter. Otherwise signal attenuation can cause data errors, and data errors will make the Mac blank out the display.

they don't seem to be quite as rare as you say

Monoprice USB-C to Mini DisplayPort Cable - 32.4Gbps Active 8K60Hz Thunderbolt 4/3 Compatible, Black, 3f -- US$39.99

OR

Monoprice Select Series USB-C to Mini Monoprice Select Series USB-C to Mini DisplayPort Adapter -- US$16.99 Adapter

and

Monoprice Select Series Monoprice Select Series DisplayPort 1.4 Cable, 3ft Black --US$7.59 1.4 Cable, 3ft Black

alex-ya wrote:

From the monitor's user guide page 11 (as you mentioned), the last line in the table - "3840 x 2160 60 Hz (DP source only)*", it seems that if the source is not DP, it can't support 4K@60hz.

The monitor user guide is referring to the ports on the monitor – not to the ports on your computer. It is saying that if you hook up the monitor using the monitor's HDMI input, you won't get 4K@60Hz.

My cable is type-c to mini-DP, the source is type-c, not DP.

If you're using a USB-C to Mini DisplayPort adapter cable, with the Mini DisplayPort end plugged into the monitor, you are, as far as the monitor is concerned, providing DisplayPort input.

Also, check the monitor menus, and make sure that DisplayPort 1.2 is enabled on the monitor.

I get the impression from pages 10 and 34-35 of the manual that the monitor won't support 3840x2160 @ 60 Hz unless you use the DisplayPort input and that option is enabled.

alex-ya wrote:

This weekend, I acquired a 1.5m DP to miniDP cable to connect my PC (DP port) to my monitor (miniDP). It successfully supports 4K resolution at 60Hz. Therefore, I suspect the issue might lie within the settings of the MacBook Pro M3 Pro.

My understanding is that recent versions of macOS do not like to see display transmission errors. If macOS sees errors, it may deliberately cut resolution or cut signal.

Windows and old versions of macOS might be less picky about errors – continuing to transmit a signal even when there are transmission errors and there is a potential for noticeable artifacts on the display.

Mr. Bennet-Alder can probably elaborate.

Monoprice (US west coast) is a low cost supplier that is distinctive because they have some idea of what they are selling, and how it should perform.

when you say not available "here" what market is "here" ??

the cables "shipped in the box" are Notorious for being 'lowest bidder' cables, and are often freely substituted for even cheaper cables at the factory. They tend to be just good enough to get you picture so that you don't return the device the same day.

Many E-commerce sellers in the US have a similar problem. They offer what is inexpensive and in great demand, not necessarily what is the best for certain displays.

Perhaps good cables for high-end hi-color displays are a specialty item, and only available through video specialty sellers.