4K Monitor Only Displaying 2560x1440p

Okay, MattLens, since you don’t have an m1/m2 Mac ( Apple silicon) you can do something, try this first :

reset smc/pmu and zap pram 3-4 times on startup per this link : https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html then see what’s going on..I presume you know that holding down the “option” key while going into system prefs> display/ monitor will get you the scaled for display choice every time…

John b

to use that 4K display on a USB-C cable, the cable length must be limited to under 1 meter in total length.

Otherwise, errors may be detected by a Modern Mac running recent macOS, and the resolution will be automatically reduced. You Might get higher resolution if you select a lower refresh rate.

For genuine ThunderBolt displays (this is not one), maximum cable length is 0.8 meters for Apple cables, 0.5 meters for brand-X cables.

do you have another cable to try?

• Inputs: DisplayPort, HDMI, USB type C

Monoprice Consul Series USB-C DisplayPort Adapter - Product # 35503 - $17.97  



if no joy, you may need to contact support:

Official Apple Support

You left out the key issue that is causing you grief.

When you chose to Mirror Displays, a 'compromise' resolution is computed, which is expected to be attainable by both displays, and BOTH are run from a single display-generator in perfect unison.

the two blue Icons for two displays are nearly co-incident, indicating Mirrored.

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if you want to be able to reach the top resolutions, the displays must be independent,

Extended Desktop:

Yes sure you set aside the two meter cable and do not use it for your highest-resolution displays.

The built-in display is 2880 by 1800.

That is suspiciously close to 2560 by 1400 shown as the top resolution for the External display. but as long as you select 'Extended desktop' and Not 'Mirror displays' each display should be able to use its top native resolution.

If you flip the switch in displays preferences to "show all resolutions", do you get any higher ones?

if you have set your external display to MIRROR your internal display, then both displays will be set the the EXACT same computed resolution, and will be refreshed in lock-step with the same display-generator hardware. That is expected behavior.

only by using your second display as an extension of the built-in display, as one big "extended desktop" will the resolution be allowed to go as high as the native resolution of the external display, like this:

the cable you cited on Amazon is a TWO meter cable.

the required cable for top performance is a ONE meter or shorter cable.

so YES! you need a better cable!

then when you click "show all resolutions" do you get any more?

that is a very good cable, IF it is operating correctly.

The requirement is for at least a USB-C 3.1 rated Cable, clearly labeled USB SuperSpeed+ logo at each end, under 1 meter in length.

The speed doubling to USB 3.2 speeds is accomplished by "turning around" the inbound data pathways into outbound pathways to double the speed, essentially "in software". So USB 3.1 and USB 3.2 cables are identical, provided they are rated at least SuperSpeed+

Works on USB-C to DisplayPort but not with a Thunderbolt cable suggests the cable, the display's USB-C port, or or the Mac may be broken. Cable failure is more likely, and easier to determine.

I posted older versions because they 'talk to me' in a very Visceral way, something the changes in Ventura do Not accomplish.

Your latest screenshot is different from the ones you posted earlier (which showed the same picture on each display).

What happens when you select "extend displays" off that drop-down menu featured prominently in your screenshot?