Mac Mini M4 Showing Monitor Resolutions Higher than Max

[Engender]

Does anyone know why MacOS (15.7.5) shows that monitors are 4K when they're really not? I have two DELL U2518Ds, which are 1440p, but MacOS says the resolution is 4K, as you can see from the below.

Also, if I did purchase 4K monitors to replace my current Dells, would I just end up running them at 1080p, like I am with my 1440p monitors?

 

[Fishrrman]

I will take a GUESS that it's a "reporting glitch" in either the hardware (cable) or software (identifying signal or code sent from display to Mac to convey what size the display is and what signal to send).

You asked:
"Also, if I did purchase 4K monitors to replace my current Dells, would I just end up running them at 1080p, like I am with my 1440p monitors?"

You could use them at a number of different resolutions -- which one you choose is up to you.

The Mac will see them as 4k and offer the "default" resolution of "looks like 1080p" (HiDPI mode with pixel "doubling" in each direction). But you're not locked into that.

I have a Dell Ultrasharp 27" 4k, and I also use the "Better Display Pro" utility with it (and my m4 Mini). I started with "looks like 1080p", but found that with Better Display I could also get a very fine image at 2048x1152 (one "step" higher).

BD (it runs in both "free mode" and "pay for" mode) also offers you menu-bar control of the display's settings (many of which are not available using only Apple's settings pane):

 

[Engender]

I've got better display. That's how I have my center monitor, the non-Dell one, at 2128 x 1197. That allows windows to maintain the same size as I move them from monitor to monitor.

 

[Engender]

Interestingly, I've been experimenting with USBC to HDMI and USBC to DP connections with the Dell monitors, and the higher resolutions have appeared throughout.

 

[!!!]

I've got better display.

I think that's the reason. I have a 1080p display and Better Display and System Profiler also claims my display is 4K.

 

[Engender]

Interesting! Have you reported that to BetterDisplay? Maybe it's a BetterDisplay bug?