Imac Pro resolution problem!

Can you select the 5120 x 2880 resolution..?

What happens when you turn On and turn Off Show all resolutions..?

If not... Shutdown > Startup in Safe Mode > Login > Restart Normally > Revisit the Display Settings.

see > Use safe mode on your Mac - Apple Support

As for the Retina "2880x1620" and "3200x1800" choices, those let you crowd a little more text and objects onto the screen, at the expense of text and object sizes.

Like the Retina "2560x1440" choice, these two choices take advantage of the full 5K resolution of the LCD panel. But the scaling is not exact. E.g., if you select "2880x1620", I believe the Mac would

• Use 2880x1620 for sizing
• Draw on a 5760x3240 canvas
• Downscale the contents of the 5760x3240 canvas to fit on the 5120x2880 pixel LCD panel

Your System Information display does not have a "UI Looks like" line. I'm guessing that this is a Sonoma change (I'm still on Ventura). Sonoma is apparently being a little less transparent …

The "Resolution" line suggests that your Mac is drawing on a "Retina 5K (5120x2880)" canvas.

If you

• Go into System Settings > Displays
• Select "2560x1440 (low resolution)" (from the All Resolutions list)
• Go into System Information
• Do a File > Refresh Information

you'll probably see the System Information "Resolution" change to "2560 x 1440 (QHD/WQHD - Wide Quad High Definition)", or some variant thereof.

Another thing you can play with (if interested):

If you look at text on the screen while going back and and forth between the "2560 x 1440" and "2560 x 1440 (low resolution)" settings, you will probably see text getting fuzzy when you switch to the (low resolution)" one, and getting sharper when you switch to the regular (Retina) one.

If you run System Information ( > System Information… ), things may become a little clearer.

I'm running a 4K monitor in Retina "UI looks like 2560x1440" mode. In Settings > Displays, this mode shows up as "2560x1440" (no "(low resolution)" qualifier) or the icon one notch down from "Larger Text".

The monitor reports that it receives a 4K signal from the computer.

If a 27" iMac Pro is running in Retina "UI looks like 2560x1440" mode, that is not a problem.

That would be the normal mode for that machine. The 2560x1440 is for sizing. Retina-aware applications would draw on an internal canvas with twice the number of pixels in each direction (i.e., a 5120x2880 canvas). The Mac would display the contents of the 5120x2880 pixel canvas on the 5120x2880 LCD pixel LCD panel.

If everything gets really small when one selects 5120x2880, that also would be to expected. In that mode you are displaying the equivalent of a 2x2 stack of 27" 2560x1440 screens in the amount of physical area that a single 27" 2560x1440 screen normally takes. You get 4x as much workspace, but everything takes up 1/4th of the area. This is why Apple came out with Retina modes in the first place. Once PPI gets high enough, it does not make sense to put all pixels towards more workspace, any more than it makes sense to print books in 2- and 3-point fonts.

You would want to avoid "2560x1440 (low-res)" mode, where the machine draws on a 2560x1440 canvas and then does an ugly digital zoom to paint the 5120x2880 screen. I suspect that you have to "Show all resolutions" to even see the "(low-res)" modes as choices.

OK next restart holding the Option, Command, P, R keys to reset the NVRAM.

see > Reset NVRAM on your Mac - Apple Support

You're welcome. Sorry that nothing we tried helped..

Next step, is to report the issue directly to Apple using Feedback.

see > Feedback - macOS - Apple

and > Feedback - iMac - Apple